Methods and Systems for Damping Oscillations of a Payload

ABSTRACT

Described herein are methods and systems to dampen oscillations of a payload coupled to a tether of a winch system arranged on an unmanned aerial vehicle (UAV). For example, the UAV&#39;s control system may dampen the oscillations by causing the UAV to switch to a forward flight mode in which movement of the UAV results in drag on the payload, thereby damping the oscillations. In another example, the control system may cause the UAV to reduce an extent flight stabilization along at least one dimension, thereby resulting in damping of the detected oscillations due to energy dissipation during movement of the UAV along the dimension. In this way, the control system could select and carry out one or more such techniques, and could do so during retraction and/or deployment of the tether.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.15/389,290, filed Dec. 22, 2016, which claims priority to U.S.Provisional patent application Ser. No. 62/385,856 filed on Sep. 9, 2016and entitled “Methods and Systems for Damping Oscillations of aPayload,” both of which are herein incorporated by reference in theirentirety and for all purposes.

BACKGROUND

An unmanned vehicle, which may also be referred to as an autonomousvehicle, is a vehicle capable of travel without a physically-presenthuman operator. An unmanned vehicle may operate in a remote-controlmode, in an autonomous mode, or in a partially autonomous mode.

When an unmanned vehicle operates in a remote-control mode, a pilot ordriver that is at a remote location can control the unmanned vehicle viacommands that are sent to the unmanned vehicle via a wireless link. Whenthe unmanned vehicle operates in autonomous mode, the unmanned vehicletypically moves based on pre-programmed navigation waypoints, dynamicautomation systems, or a combination of these. Further, some unmannedvehicles can operate in both a remote-control mode and an autonomousmode, and in some instances may do so simultaneously. For instance, aremote pilot or driver may wish to leave navigation to an autonomoussystem while manually performing another task, such as operating amechanical system for picking up objects, as an example.

Various types of unmanned vehicles exist for various differentenvironments. For instance, unmanned vehicles exist for operation in theair, on the ground, underwater, and in space. Examples includequad-copters and tail-sitter UAVs, among others. Unmanned vehicles alsoexist for hybrid operations in which multi-environment operation ispossible. Examples of hybrid unmanned vehicles include an amphibiouscraft that is capable of operation on land as well as on water or afloatplane that is capable of landing on water as well as on land. Otherexamples are also possible.

SUMMARY

Example implementations may relate to various techniques for dampingoscillations of a payload coupled to a tether of a winch system arrangedon an unmanned aerial vehicle (UAV). For example, the UAV's controlsystem may dampen the oscillations by causing the UAV to switch to aforward flight mode in which movement of the UAV results in drag on thepayload, thereby damping the oscillations due to the drag. In anotherexample, the control system may cause the UAV to reduce an extent offlight stabilization along at least one dimension, thereby resulting indamping of the detected oscillations due to energy dissipation duringmovement of the UAV along the at least one dimension. In this way, thecontrol system could select and carry out one or more such techniques,and could do so during retraction and/or deployment of the tether.

In one aspect, a system is provided. The system may include a winchsystem for an aerial vehicle, where the winch system includes: (a) atether disposed on a spool, (b) a motor that is operable to apply torqueto the tether, and (c) a payload coupling apparatus coupled to a leadingend of the tether and structured to mechanically couple a payload to thetether. The system may also include a control system operable to, whilethe aerial vehicle is in a hover flight mode, switch to operation in atether retraction mode. The control system is also operable to, whileoperating in the tether retraction mode, perform a damping routine todampen oscillations of the payload coupling apparatus.

In another aspect, another system is provided. The system may include awinch system for an aerial vehicle, where the winch system includes: (a)a tether disposed on a spool and (b) a motor that is operable to applytorque to the tether. The system may also include a control systemoperable to, while the aerial vehicle is in a hover flight mode, causethe aerial vehicle to switch from the hover flight mode to a forwardflight mode in which movement of the aerial vehicle results in drag on apayload that is coupled to the tether, where the drag dampensoscillations of the payload when the tether is at least partiallyunwound.

In yet another aspect, yet another system is provided. The system mayinclude a winch system for an aerial vehicle, where the winch systemincludes: (a) a tether disposed on a spool and (b) a motor that isoperable to apply torque to the tether, and where the aerial vehicle isoperable in a position-hold mode in which the aerial vehiclesubstantially maintains a physical position during hover flight byengaging in flight stabilization along three dimensions in physicalspace. The system may also include a control system operable to, whilethe aerial vehicle is in the position-hold mode, cause the aerialvehicle to reduce an extent of flight stabilization along at least oneof the three dimensions, thereby resulting in damping of oscillations ofa payload due to energy dissipation during movement of the aerialvehicle along the at least one dimension, where the payload is coupledto the tether, and where the oscillations occur when the tether is atleast partially unwound.

In yet another aspect, yet another system is provided. The system mayinclude a winch system for an aerial vehicle, where the winch systemincludes: (a) a tether disposed on a spool and (b) a motor that isoperable to apply torque to the tether. The system may also include acontrol system operable to, while the tether is at least partiallyunwound, select one or more damping routines from a plurality ofavailable damping routines to dampen oscillations of a payload that iscoupled to the tether. The control system is also operable to performthe one or more selected damping routines.

In yet another aspect, yet another system is provided. The system mayinclude means for, while an aerial vehicle is in a hover flight mode,switching to operation in a tether retraction mode. The system may alsoinclude means for, while operating in the tether retraction mode,performing a damping routine to dampen oscillations of a payloadcoupling apparatus.

In yet another aspect, yet another system is provided. The system mayinclude means for, while an aerial vehicle is in a hover flight mode,causing the aerial vehicle to switch from the hover flight mode to aforward flight mode in which movement of the aerial vehicle results indrag on a payload that is coupled to a tether, where the drag dampensoscillations of the payload when the tether is at least partiallyunwound.

In yet another aspect, yet another system is provided. The system mayinclude means for, while the aerial vehicle is in a position-hold mode,causing the aerial vehicle to reduce an extent of flight stabilizationalong at least one of three dimensions, thereby resulting in damping ofoscillations of a payload due to energy dissipation during movement ofthe aerial vehicle along the at least one dimension, where the payloadis coupled to a tether, and where the oscillations occur when the tetheris at least partially unwound.

In yet another aspect, yet another system is provided. The system mayinclude means for, while the tether is at least partially unwound,selecting one or more damping routines from a plurality of availabledamping routines to dampen oscillations of a payload that is coupled toa tether. The system may also include means for performing the one ormore selected damping routines.

These as well as other aspects, advantages, and alternatives will becomeapparent to those of ordinary skill in the art by reading the followingdetailed description with reference where appropriate to theaccompanying drawings. Further, it should be understood that thedescription provided in this summary section and elsewhere in thisdocument is intended to illustrate the claimed subject matter by way ofexample and not by way of limitation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a simplified illustration of an unmanned aerial vehicle,according to an example embodiment.

FIG. 1B is a simplified illustration of an unmanned aerial vehicle,according to an example embodiment.

FIG. 1C is a simplified illustration of an unmanned aerial vehicle,according to an example embodiment.

FIG. 1D is a simplified illustration of an unmanned aerial vehicle,according to an example embodiment.

FIG. 1E is a simplified illustration of an unmanned aerial vehicle,according to an example embodiment.

FIG. 2 is a simplified block diagram illustrating components of anunmanned aerial vehicle, according to an example embodiment.

FIG. 3 is a simplified block diagram illustrating a UAV system,according to an example embodiment.

FIGS. 4A, 4B, and 4C show a payload delivery apparatus, according toexample embodiments.

FIG. 5A shows a perspective view of a payload delivery apparatus 500including payload 510, according to an example embodiment.

FIG. 5B is a cross-sectional side view of payload delivery apparatus 500and payload 510 shown in FIG. 5A.

FIG. 5C is a side view of payload delivery apparatus 500 and payload 510shown in FIGS. 5A and 5B.

FIG. 6A is a perspective view of payload coupling apparatus 800,according to an example embodiment.

FIG. 6B is a side view of payload coupling apparatus 800 shown in FIG.6A.

FIG. 6C is a front view of payload coupling apparatus 800 shown in FIGS.6A and 6B.

FIG. 7 is a perspective view of payload coupling apparatus 800 shown inFIGS. 6A-6C, prior to insertion into a payload coupling apparatusreceptacle positioned in the fuselage of a UAV.

FIG. 8 is another perspective view of payload coupling apparatus 800shown in FIGS. 6A-6C, prior to insertion into a payload couplingapparatus receptacle positioned in the fuselage of a UAV.

FIG. 9 shows a perspective view of a recessed restraint slot and payloadcoupling apparatus receptacle positioned in a fuselage of a UAV.

FIG. 10A shows a side view of a payload delivery apparatus 500 with ahandle 511 of payload 510 secured within a payload coupling apparatus800 as the payload 510 moves downwardly prior to touching down fordelivery.

FIG. 10B shows a side view of payload delivery apparatus 500 afterpayload 510 has landed on the ground showing payload coupling apparatus800 decoupled from handle 511 of payload 510.

FIG. 10C shows a side view of payload delivery apparatus 500 withpayload coupling apparatus 800 moving away from handle 511 of payload510.

FIG. 11 is a side view of handle 511 of payload 510.

FIG. 12 shows a pair of locking pins 570, 572 extending through holes514 and 516 in handle 511 of payload 510 to secure the handle 511 andtop of payload 510 within the fuselage of a UAV.

FIG. 13A is a perspective view of payload coupling apparatus 900 priorto having a handle of a payload positioned within slot 920 of payloadcoupling apparatus 900.

FIG. 13B is a perspective view of payload coupling apparatus 900 afterdelivering a payload and decoupling from a handle of a payload.

FIG. 14A is a front perspective view of payload coupling apparatus 900shown in FIGS. 13A and 13B, according to an example embodiment.

FIG. 14B is a rear perspective view of payload coupling apparatus 900shown in FIG. 14A.

FIG. 14C is a side view of payload coupling apparatus 900 shown in FIGS.14A and 14B.

FIG. 14D is a front view of payload coupling apparatus 900 shown inFIGS. 14A-14C.

FIG. 14E is a top view of payload coupling apparatus 900 shown in FIGS.14A-D.

FIG. 15A is a perspective view of payload coupling apparatus 1000,according to an example embodiment.

FIG. 15B is another perspective view of payload coupling apparatus 1000shown in FIG. 15A.

FIG. 15C is a side view of payload coupling apparatus 1000 shown inFIGS. 15A and 15B.

FIG. 15D is a top view of payload coupling apparatus 1000 shown in FIGS.15A-C.

FIG. 15E is a cross-sectional side view of payload coupling apparatus1000 shown in FIGS. 15A-D.

FIG. 16A is a side view of payload coupling apparatus 800′ with a slot808 positioned above lip 806′, according to an example embodiment.

FIG. 16B is a side view of payload coupling apparatus 800′ after slot808 has been closed following decoupling of payload coupling apparatus800′ from a handle of a payload.

FIG. 16C is a cross-sectional side view of payload coupling apparatus800′ shown in FIG. 16A.

FIG. 16D is a cross-sectional side view of payload coupling apparatus800′ shown in FIG. 16B.

FIG. 17 is a flow chart of a method for carrying out tethered pickup ofa payload for subsequent delivery to a target location, according to anexample embodiment.

FIG. 18 is a flow chart of a method for carrying out tethered deliveryof a payload, according to an example embodiment.

FIG. 19 is an example flowchart for facilitating control of the tetherfor purposes of interacting with and/or providing feedback to a user,according to an example embodiment.

FIG. 20 illustrates a motor current level over time, according to anexample embodiment.

FIG. 21 illustrates a detected current spike that is indicative of aparticular user-interaction with a tether, according to an exampleembodiment.

FIG. 22 illustrates a motor response based on the particularuser-interaction, according to an example embodiment.

FIG. 23 illustrates a motor response process to adjust tension of thetether, according to an example embodiment.

FIG. 24 illustrates a motor response process to provide the feel of adetent, according to an example embodiment.

FIG. 25 illustrates a motor response process followed by a UAV responseprocess, according to an example embodiment.

FIG. 26 is a flow chart of a method for determining whether a payloadhas detached from a tether of a UAV, according to an example embodiment.

FIG. 27 is an example flowchart for initiating a damping routine todampen oscillations of a payload coupling apparatus, according to anexample embodiment.

FIGS. 28A to 28D collectively illustrate initiation of a damping routineduring a tether retraction process, according to an example embodiment.

FIG. 29 is an example flowchart for initiating forward flight to dampenoscillations of a payload, according to an example embodiment.

FIGS. 30A to 30D collectively illustrate use of forward flight to dampenoscillations of a payload, according to an example embodiment.

FIG. 31 is an example flowchart for reducing an extent of flightstabilization to dampen oscillations of a payload, according to anexample embodiment.

FIGS. 32A to 32H collectively illustrate use of reduction in the extentof flight stabilization to dampen oscillations of a payload, accordingto an example embodiment.

FIG. 33 is an example flowchart for selecting one or more dampingroutines to help dampen oscillations of a payload, according to anexample embodiment.

FIG. 34 is a flow chart of a method for detaching a tether from a UAV,according to an example embodiment.

FIG. 35 is a flow chart of a method for detecting and addressingdownward forces on a tether when lowering a payload toward the ground,according to an example embodiment.

FIG. 36 is a flow chart of a method for detecting and addressingdownward forces on a tether when winching a payload toward a UAV,according to an example embodiment.

FIG. 37 is a flow chart of a method for detecting whether a UAV hassuccessfully picked up a payload, according to an example embodiment.

FIG. 38A illustrates a portion of a state diagram of a UAV carrying outa payload pickup and delivery process, according to an exampleembodiment.

FIG. 38B illustrates another portion of the state diagram of a UAVcarrying out a payload pickup and delivery process, according to anexample embodiment.

FIG. 38C illustrates another portion of the state diagram of a UAVcarrying out a payload pickup and delivery process, according to anexample embodiment.

DETAILED DESCRIPTION

Exemplary methods and systems are described herein. It should beunderstood that the word “exemplary” is used herein to mean “serving asan example, instance, or illustration.” Any implementation or featuredescribed herein as “exemplary” or “illustrative” is not necessarily tobe construed as preferred or advantageous over other implementations orfeatures. In the figures, similar symbols typically identify similarcomponents, unless context dictates otherwise. The exampleimplementations described herein are not meant to be limiting. It willbe readily understood that the aspects of the present disclosure, asgenerally described herein, and illustrated in the figures, can bearranged, substituted, combined, separated, and designed in a widevariety of different configurations, all of which are contemplatedherein.

I. OVERVIEW

The present embodiments are related to the use of unmanned aerialvehicles (UAVs) or unmanned aerial systems (UASs) (referred tocollectively herein as UAVs) that are used to carry a payload to bedelivered or retrieved. As examples, UAVs may be used to deliver orretrieve a payload to or from an individual or business. In operationthe payload to be delivered is secured to the UAV and the UAV is thenflown to the desired delivery site. Once the UAV arrives at the deliverysite, the UAV may land to deliver the payload, or operate in a hovermode and lower the payload from the UAV towards the delivery site usinga tether and a winch mechanism positioned with the UAV. Upon touchdownof the payload, a payload coupling apparatus, sometimes referred to as a“capsule,” is automatically decoupled from the payload. In addition, thepayload may be retrieved while the UAV is operating in a hover mode bypositioning a handle of the payload into a slot in the payload couplingapparatus.

In order to deliver the payload, the UAV may include various mechanismsto secure the payload during transport and release the payload upondelivery. Example embodiments may take the form of or otherwise relateto an apparatus for passively coupling a payload to a UAV for transportand releasing the payload upon delivery.

Such a payload coupling apparatus may include a housing coupled to theUAV by a tether that may be wound and unwound to raise and lower thehousing with respect to the UAV. The housing may include one or moreswing arms adapted to extend from the housing at an acute angle, forminga hook on which the payload may be attached. When the housing andattached payload are lowered from the UAV (e.g., by unwinding thetether) to a transport location below the UAV (e.g., the ground), thepayload may detach from the hook.

For instance, once the payload reaches the ground, the UAV may over-runthe tether by continuing to unwind the tether. As the payload remainsstationary on the ground, the payload coupling apparatus may continue tolower, and a gravitational and/or an inertial force on the housing maycause the swing arm hook to detach from the payload. Upon detaching fromthe payload, the swing arm may be adapted to retract into the housing,and the payload coupling apparatus may ascend (e.g., by retracting thetether) toward the UAV, leaving the payload on the ground. As thepayload coupling apparatus approaches the UAV, a device adapted toreceive the housing may engage a cam of the swing arm causing the swingarm to extend from the housing at an acute angle, thereby forming a hookfor securing another payload for delivery by the UAV.

More specifically, the present embodiments advantageously include aunique payload coupling apparatus. In one embodiment, the payloadcoupling apparatus includes a slot downwardly extending from an outersurface of the payload coupling apparatus towards a center of thepayload coupling apparatus. The slot is adapted to receive a handle of apayload, and supports the payload during delivery or retrieval of thepayload. Once the payload reaches the ground, the payload couplingapparatus continues to move downwardly until the handle of the payloadis decoupled from the slot of the payload coupling apparatus. An outersurface of a lower lip beneath the slot is undercut such that it extendsless than the outer surface of the upper end of the payload couplingdevice above the slot to prevent the payload coupling device fromreengaging with the handle of the payload during retrieval of thepayload coupling device to the UAV, or with catching on power lines ortree branches.

The payload coupling apparatus may include cams positioned on oppositesides of an outer surface thereof. As the payload coupling apparatus iswinched back to the UAV, the cams of the payload coupling apparatus areadapted to engage with corresponding cams within the fuselage of the UAVsuch that when the cams engage, the payload coupling apparatus is ableto rotate to orient the payload coupling apparatus in a desired positionwithin the fuselage of the UAV.

In this regard, the payload may have a longitudinally extending top suchthat when the cams on the outer surface of the payload couplingapparatus engage the mating cams within the fuselage of the UAV, thelongitudinally extending top is rotated into a desired position within acorresponding longitudinally extending recessed restraint slot in thebottom of the fuselage of the UAV. In other embodiments, the payload maybe simply drawn into a tight positioning against the bottom of thefuselage of the UAV. In such cases, the top of the payload is notrequired to have a longitudinally extending top that becomes positionedwithin a cavity in the fuselage when the cams of the payload couplingapparatus are in engagement with mating cams within the fuselage.However, where cams are used, the cams of the payload coupling apparatusand the mating cams within a payload coupling receptacle in the fuselagemay properly rotate the payload coupling apparatus to orient the payloadin a desired position with respect to the fuselage.

A significant advantage of the payload coupling apparatus is that thepayload coupling apparatus includes no moving parts, thereby reducingits complexity and reducing the possibility of part failure which existswhen moving parts are involved in a payload coupling apparatus.

The payload may advantageously include a handle that is well-suited forpositioning within the slot of the payload coupling apparatus. Thehandle may be constructed of a thin, flexible plastic material having ahigh degree of flexibility allowing for easy insertion into the slot ofthe payload coupling mechanism, and also for easy decoupling from theslot of the payload coupling mechanism upon landing of the payload.Handle flexibility is desirable to allow the payload and payloadcoupling apparatus to hang vertically straight as the handle bends tomatch the angle of the slot in the payload coupling apparatus. A morerigid handle makes it easier for the payload coupling apparatus todecouple from the handle upon package landing, although it the handle istoo flexible the payload coupling apparatus could flip over and notrelease. Furthermore, it is desirable that upon decoupling, the handleshould spring back to a vertical orientation which further reduces there-hooking of the handle with the slot of the payload couplingapparatus, and to pull the package tight into the restraint whenengaging within the fuselage of the UAV. It should also be noted thatthe handle could also be out of paper or other natural fiber, with orwithout plastic lamination or plastic/glass/natural fibers for extrastrength. As an example, fiber reinforced paper may be used as well.

The handle may also advantageously include a pair of holes that areadapted to receive locking pins positioned within the UAV. The lockingpins may have a conical shape to facilitate insertion into the holes inthe handle and to pull the package into tight engagement within therecessed restraint slot in the fuselage of the UAV. Once the cams of thepayload coupling apparatus are engaged with the mating cams within thefuselage, the handle is positioned in the desired orientation. A servomotor or other mechanism such as a regular electric motor with aleadscrew, or rack and pinion with limit switches to control travel (orother mechanism such as a linear actuator) may be used to move theconical locking pins through the holes in the handle to hold the handleand payload beneath tightly in position, allowing for high speed flightof the UAV when the payload is secured beneath the UAV. Alternatively,the locking pins or pin could be moved into position within a recess oropening in the payload coupling apparatus itself, rather than into holesin the handle of the of the package to secure the payload couplingapparatus and package to the UAV.

The payload may take the form of an aerodynamic tote, although thepayload may have any number of different configurations and geometries.However, where a linear recessed restraint slot is positioned with thefuselage, it is desirable that the top of the payload has a generallylinear shape to fit within the linear recessed restraint slot within thefuselage.

The payload coupling mechanism may have different configurations aswell. For example, a tether may be attached to a bottom of the payloadcoupling apparatus, and is positioned within a vertically extendingtether slot in the payload coupling apparatus. The vertical tether slotextends through the payload coupling apparatus that is adapted toreceive a handle of a payload. In this position, the handle of thepayload is positioned within the slot during delivery and retrieval. Thepayload coupling apparatus also includes a pair of upwardly extendingfingers positioned about the slot with an opening between the pair offingers.

When the payload touches the ground, the payload coupling apparatuscontinues to move downwardly and automatically is decoupled from thehandle of the payload. The payload coupling apparatus may include a tophalf that is weighted, such that upon decoupling from the handle of thepayload, the payload coupling apparatus tips over and rotates 180degrees such that the pair of upwardly extending fingers are rotated 180and extend downwardly. During this rotation, the tether becomesdisengaged from the vertical tether slot and moves through the openingbetween the pair of fingers. As a result, the payload coupling isprevented from reengaging with the handle of the payload because theslots extends downwardly. In addition, the downwardly extending slotafter release of the handle also helps to prevent the payload couplingapparatus from engaging with power lines or tree branches as it iswinched back to the UAV, because the opening in the slot extendsdownwardly. Alternately, the payload coupling apparatus may be bottomweighted.

This embodiment of the payload coupling apparatus may also include camson an outer surface thereof adapted to engage mating cams within apayload coupling apparatus receptacle within the fuselage to orient thepayload coupling apparatus in a desired position within the fuselage ofthe UAV.

In another embodiment, a vertical slot may be positioned within thepayload coupling apparatus adapted to receive a handle of a payload andto support the handle and payload during delivery and retrieval. In thisembodiment, a tether slot is positioned on an exterior of the payloadcoupling apparatus, and the top of the payload coupling apparatus isweighted such that when the payload reaches the ground, the payloadcoupling apparatus continues to move downwardly until the handle isdecoupled from the slot of the payload coupling apparatus. Oncedecoupled, the weighted payload coupling mechanism rotates 90 degreessuch that the slot cannot reengage with the handle of the payload duringretrieval or catch on power lines or tree branches. This embodiment ofthe payload coupling mechanism may include cams on an outer surfacethereof adapted to engage mating cams within the fuselage of the UAV toorient the payload coupling mechanism, and the handle and payload, in adesired position.

In addition, the payload delivery system automatically aligns thepackage during winch up, orienting it for minimum drag along theaircraft's longitudinal axis. This alignment enables high speed forwardflight after pick up. The alignment is accomplished through the shape ofthe payload hook and receptacle. The hook (also called capsule due toits shape) has cam features around its perimeter which always orient itin a defined direction when it engages into the cam features inside thereceptacle of the fuselage of the UAV. The tips of the cam shapes onboth sides of the capsule are asymmetric to prevent jamming in the 90degree orientation. In this regard, helical cam surfaces may meet at anapex on one side of the payload coupling mechanism, and helical camsurfaces may meet at a rounded apex on the other side of the payloadcoupling mechanism. The hook is specifically designed so that thepackage hangs in the centerline of the hook, enabling alignment in bothdirections from 90 degrees.

Besides the alignment functionality, the payload hook also releases thepackage passively and automatically when the package touches the groundupon delivery. This is accomplished through the shape and angle of thehook slot and the corresponding handle on the package. The hook slidesoff the handle easily when the payload touches down due to the mass ofthe capsule and also the inertia wanting to continue moving the capsuledownward past the package. The end of the hook is designed to berecessed slightly from the body of the capsule, which prevents the hookfrom accidentally re-attaching to the handle. After successful release,the hook gets winched back up into the aircraft. All this functionality(package alignment during pickup and passive release during delivery)may advantageously be achieved without any moving parts in this hookembodiment (referred to as a solid state design). This greatly increasesreliability and reduces cost. The simple design also makes userinteraction very clear and self-explanatory. In addition, the payloadcoupling apparatus may be bottom weighted so that it remains in adesired vertical orientation and does not tilt.

The package used for the winch up/pick up operation may be anaerodynamically shaped tote with a reinforced snap-in handle (e.g. madeout of plastic or other materials such as fiber), although other shapedpayloads may also be used. The handle of the payload attaches thepayload to the hook of a payload coupling apparatus and its slot oropening is shaped to allow for a reliable passive release. The handlealso may include two smaller openings for locking pins. Thereinforcement of the handle is beneficial to transmit the torque fromthe capsule into the package during the alignment rotation. The packageitself may be made out of cardstock and have an internal tear strip. Thethin fiber tape tear strip may run along the perimeter of one packageside and enables the customer to open the package easily after delivery.

When the payload is winched up and alignment is completed, the payloadis pulled into a recessed restraint slot in the fuselage of the UAV,using the additional vertical travel of the capsule in its receptacle.The recessed restraint slot matches the shape of the upper portion ofthe payload and stabilizes it during cruise flight, preventing anyexcess side to side or back and forth sway motion. The recessedrestraint slot is also completely recessed into the fuselage and has noprotruding parts, allowing for good aerodynamics on the return flight(after the package has been delivered).

The present embodiments provide a highly integrated winch-based pickupand delivery system for UAVs. A number of significant advantages may beprovided. For example, the ability to pick up and deliver packageswithout the need for landing is provided. The system is able to winch upa package with the aircraft hovering. There also may be no need forinfrastructure at the merchant or customer in certain applications. Theadvantages include high mission flexibility and the potential forlimited or no infrastructure installation costs, as well as increasedflexibility in payload geometry.

II. ILLUSTRATIVE UNMANNED VEHICLES

Herein, the terms “unmanned aerial vehicle” and “UAV” refer to anyautonomous or semi-autonomous vehicle that is capable of performing somefunctions without a physically present human pilot.

A UAV can take various forms. For example, a UAV may take the form of afixed-wing aircraft, a glider aircraft, a tail-sitter aircraft, a jetaircraft, a ducted fan aircraft, a lighter-than-air dirigible such as ablimp or steerable balloon, a rotorcraft such as a helicopter ormulticopter, and/or an ornithopter, among other possibilities. Further,the terms “drone,” “unmanned aerial vehicle system” (UAVS), or “unmannedaerial system” (UAS) may also be used to refer to a UAV.

FIG. 1A is a simplified illustration providing various views of a UAV,according to an example embodiment. In particular, FIG. 1A shows anexample of a fixed-wing UAV 1100 a, which may also be referred to as anairplane, an aeroplane, a biplane, a glider, or a plane, among otherpossibilities. The fixed-wing UAV 1100 a, as the name implies, hasstationary wings 1102 that generate lift based on the wing shape and thevehicle's forward airspeed. For instance, the two wings 1102 may have anairfoil-shaped cross section to produce an aerodynamic force on the UAV1100 a.

As depicted, the fixed-wing UAV 1100 a may include a wing body orfuselage 1104. The wing body 1104 may contain, for example, controlelectronics such as an inertial measurement unit (IMU) and/or anelectronic speed controller, batteries, other sensors, and/or a payload,among other possibilities. The illustrative UAV 1100 a may also includelanding gear (not shown) to assist with controlled take-offs andlandings. In other embodiments, other types of UAVs without landing gearare also possible.

The UAV 1100 a further includes propulsion units 1106 positioned on thewings 1106 (or fuselage), which can each include a motor, shaft, andpropeller, for propelling the UAV 1100 a. Stabilizers 1108 (or fins) mayalso be attached to the UAV 1110 a to stabilize the UAV's yaw (turn leftor right) during flight. In some embodiments, the UAV 1100 a may be alsobe configured to function as a glider. To do so, UAV 1100 a may poweroff its motor, propulsion units, etc., and glide for a period of time.In the UAV 1100 a, a pair of rotor supports 1110 extend beneath thewings 1106, and a plurality of rotors 1112 are attached rotor supports1110. Rotors 1110 may be used during a hover mode wherein the UAV 1110 ais descending to a delivery location, or ascending following a delivery.In the example UAV 1100 a, stabilizers 1108 are shown attached to therotor supports 1110.

During flight, the UAV 1100 a may control the direction and/or speed ofits movement by controlling its pitch, roll, yaw, and/or altitude. Forexample, the stabilizers 1108 may include one or more rudders 1108 a forcontrolling the UAV's yaw, and the wings 1102 may include one or moreelevators for controlling the UAV's pitch and/or one or more ailerons1102 a for controlling the UAV's roll. As another example, increasing ordecreasing the speed of all the propellers simultaneously can result inthe UAV 1100 a increasing or decreasing its altitude, respectively.

Similarly, FIG. 1B shows another example of a fixed-wing UAV 120. Thefixed-wing UAV 120 includes a fuselage 122, two wings 124 with anairfoil-shaped cross section to provide lift for the UAV 120, a verticalstabilizer 126 (or fin) to stabilize the plane's yaw (turn left orright), a horizontal stabilizer 128 (also referred to as an elevator ortailplane) to stabilize pitch (tilt up or down), landing gear 130, and apropulsion unit 132, which can include a motor, shaft, and propeller.

FIG. 1C shows an example of a UAV 140 with a propeller in a pusherconfiguration. The term “pusher” refers to the fact that a propulsionunit 142 is mounted at the back of the UAV and “pushes” the vehicleforward, in contrast to the propulsion unit being mounted at the frontof the UAV. Similar to the description provided for FIGS. 1A and 1B,FIG. 1C depicts common structures used in a pusher plane, including afuselage 144, two wings 146, vertical stabilizers 148, and thepropulsion unit 142, which can include a motor, shaft, and propeller.

FIG. 1D shows an example of a tail-sitter UAV 160. In the illustratedexample, the tail-sitter UAV 160 has fixed wings 162 to provide lift andallow the UAV 160 to glide horizontally (e.g., along the x-axis, in aposition that is approximately perpendicular to the position shown inFIG. 1D). However, the fixed wings 162 also allow the tail-sitter UAV160 to take off and land vertically on its own.

For example, at a launch site, the tail-sitter UAV 160 may be positionedvertically (as shown) with its fins 164 and/or wings 162 resting on theground and stabilizing the UAV 160 in the vertical position. Thetail-sitter UAV 160 may then take off by operating its propellers 166 togenerate an upward thrust (e.g., a thrust that is generally along they-axis). Once at a suitable altitude, the tail-sitter UAV 160 may useits flaps 168 to reorient itself in a horizontal position, such that itsfuselage 170 is closer to being aligned with the x-axis than the y-axis.Positioned horizontally, the propellers 166 may provide forward thrustso that the tail-sitter UAV 160 can fly in a similar manner as a typicalairplane.

Many variations on the illustrated fixed-wing UAVs are possible. Forinstance, fixed-wing UAVs may include more or fewer propellers, and/ormay utilize a ducted fan or multiple ducted fans for propulsion.Further, UAVs with more wings (e.g., an “x-wing” configuration with fourwings), with fewer wings, or even with no wings, are also possible.

As noted above, some embodiments may involve other types of UAVs, inaddition to or in the alternative to fixed-wing UAVs. For instance, FIG.1E shows an example of a rotorcraft that is commonly referred to as amulticopter 180. The multicopter 180 may also be referred to as aquadcopter, as it includes four rotors 182. It should be understood thatexample embodiments may involve a rotorcraft with more or fewer rotorsthan the multicopter 180. For example, a helicopter typically has tworotors. Other examples with three or more rotors are possible as well.Herein, the term “multicopter” refers to any rotorcraft having more thantwo rotors, and the term “helicopter” refers to rotorcraft having tworotors.

Referring to the multicopter 180 in greater detail, the four rotors 182provide propulsion and maneuverability for the multicopter 180. Morespecifically, each rotor 182 includes blades that are attached to amotor 184. Configured as such, the rotors 182 may allow the multicopter180 to take off and land vertically, to maneuver in any direction,and/or to hover. Further, the pitch of the blades may be adjusted as agroup and/or differentially, and may allow the multicopter 180 tocontrol its pitch, roll, yaw, and/or altitude.

It should be understood that references herein to an “unmanned” aerialvehicle or UAV can apply equally to autonomous and semi-autonomousaerial vehicles. In an autonomous implementation, all functionality ofthe aerial vehicle is automated; e.g., pre-programmed or controlled viareal-time computer functionality that responds to input from varioussensors and/or pre-determined information. In a semi-autonomousimplementation, some functions of an aerial vehicle may be controlled bya human operator, while other functions are carried out autonomously.Further, in some embodiments, a UAV may be configured to allow a remoteoperator to take over functions that can otherwise be controlledautonomously by the UAV. Yet further, a given type of function may becontrolled remotely at one level of abstraction and performedautonomously at another level of abstraction. For example, a remoteoperator could control high level navigation decisions for a UAV, suchas by specifying that the UAV should travel from one location to another(e.g., from a warehouse in a suburban area to a delivery address in anearby city), while the UAV's navigation system autonomously controlsmore fine-grained navigation decisions, such as the specific route totake between the two locations, specific flight controls to achieve theroute and avoid obstacles while navigating the route, and so on.

More generally, it should be understood that the example UAVs describedherein are not intended to be limiting. Example embodiments may relateto, be implemented within, or take the form of any type of unmannedaerial vehicle.

III. ILLUSTRATIVE UAV COMPONENTS

FIG. 2 is a simplified block diagram illustrating components of a UAV200, according to an example embodiment. UAV 200 may take the form of,or be similar in form to, one of the UAVs 100, 120, 140, 160, and 180described in reference to FIGS. 1A-1E. However, UAV 200 may also takeother forms.

UAV 200 may include various types of sensors, and may include acomputing system configured to provide the functionality describedherein. In the illustrated embodiment, the sensors of UAV 200 include aninertial measurement unit (IMU) 202, ultrasonic sensor(s) 204, and a GPS206, among other possible sensors and sensing systems.

In the illustrated embodiment, UAV 200 also includes one or moreprocessors 208. A processor 208 may be a general-purpose processor or aspecial purpose processor (e.g., digital signal processors, applicationspecific integrated circuits, etc.). The one or more processors 208 canbe configured to execute computer-readable program instructions 212 thatare stored in the data storage 210 and are executable to provide thefunctionality of a UAV described herein.

The data storage 210 may include or take the form of one or morecomputer-readable storage media that can be read or accessed by at leastone processor 208. The one or more computer-readable storage media caninclude volatile and/or non-volatile storage components, such asoptical, magnetic, organic or other memory or disc storage, which can beintegrated in whole or in part with at least one of the one or moreprocessors 208. In some embodiments, the data storage 210 can beimplemented using a single physical device (e.g., one optical, magnetic,organic or other memory or disc storage unit), while in otherembodiments, the data storage 210 can be implemented using two or morephysical devices.

As noted, the data storage 210 can include computer-readable programinstructions 212 and perhaps additional data, such as diagnostic data ofthe UAV 200. As such, the data storage 210 may include programinstructions 212 to perform or facilitate some or all of the UAVfunctionality described herein. For instance, in the illustratedembodiment, program instructions 212 include a navigation module 214 anda tether control module 216.

A. Sensors

In an illustrative embodiment, IMU 202 may include both an accelerometerand a gyroscope, which may be used together to determine an orientationof the UAV 200. In particular, the accelerometer can measure theorientation of the vehicle with respect to earth, while the gyroscopemeasures the rate of rotation around an axis. IMUs are commerciallyavailable in low-cost, low-power packages. For instance, an IMU 202 maytake the form of or include a miniaturized MicroElectroMechanical System(MEMS) or a NanoElectroMechanical System (NEMS). Other types of IMUs mayalso be utilized.

An IMU 202 may include other sensors, in addition to accelerometers andgyroscopes, which may help to better determine position and/or help toincrease autonomy of the UAV 200. Two examples of such sensors aremagnetometers and pressure sensors. In some embodiments, a UAV mayinclude a low-power, digital 3-axis magnetometer, which can be used torealize an orientation independent electronic compass for accurateheading information. However, other types of magnetometers may beutilized as well. Other examples are also possible. Further, note that aUAV could include some or all of the above-described inertia sensors asseparate components from an IMU.

UAV 200 may also include a pressure sensor or barometer, which can beused to determine the altitude of the UAV 200. Alternatively, othersensors, such as sonic altimeters or radar altimeters, can be used toprovide an indication of altitude, which may help to improve theaccuracy of and/or prevent drift of an IMU.

In a further aspect, UAV 200 may include one or more sensors that allowthe UAV to sense objects in the environment. For instance, in theillustrated embodiment, UAV 200 includes ultrasonic sensor(s) 204.Ultrasonic sensor(s) 204 can determine the distance to an object bygenerating sound waves and determining the time interval betweentransmission of the wave and receiving the corresponding echo off anobject. A typical application of an ultrasonic sensor for unmannedvehicles or IMUs is low-level altitude control and obstacle avoidance.An ultrasonic sensor can also be used for vehicles that need to hover ata certain height or need to be capable of detecting obstacles. Othersystems can be used to determine, sense the presence of, and/ordetermine the distance to nearby objects, such as a light detection andranging (LIDAR) system, laser detection and ranging (LADAR) system,and/or an infrared or forward-looking infrared (FLIR) system, amongother possibilities.

In some embodiments, UAV 200 may also include one or more imagingsystem(s). For example, one or more still and/or video cameras may beutilized by UAV 200 to capture image data from the UAV's environment. Asa specific example, charge-coupled device (CCD) cameras or complementarymetal-oxide-semiconductor (CMOS) cameras can be used with unmannedvehicles. Such imaging sensor(s) have numerous possible applications,such as obstacle avoidance, localization techniques, ground tracking formore accurate navigation (e,g., by applying optical flow techniques toimages), video feedback, and/or image recognition and processing, amongother possibilities.

UAV 200 may also include a GPS receiver 206. The GPS receiver 206 may beconfigured to provide data that is typical of well-known GPS systems,such as the GPS coordinates of the UAV 200. Such GPS data may beutilized by the UAV 200 for various functions. As such, the UAV may useits GPS receiver 206 to help navigate to the caller's location, asindicated, at least in part, by the GPS coordinates provided by theirmobile device. Other examples are also possible.

B. Navigation and Location Determination

The navigation module 214 may provide functionality that allows the UAV200 to, e.g., move about its environment and reach a desired location.To do so, the navigation module 214 may control the altitude and/ordirection of flight by controlling the mechanical features of the UAVthat affect flight (e.g., its rudder(s), elevator(s), aileron(s), and/orthe speed of its propeller(s)).

In order to navigate the UAV 200 to a target location, the navigationmodule 214 may implement various navigation techniques, such asmap-based navigation and localization-based navigation, for instance.With map-based navigation, the UAV 200 may be provided with a map of itsenvironment, which may then be used to navigate to a particular locationon the map. With localization-based navigation, the UAV 200 may becapable of navigating in an unknown environment using localization.Localization-based navigation may involve the UAV 200 building its ownmap of its environment and calculating its position within the mapand/or the position of objects in the environment. For example, as a UAV200 moves throughout its environment, the UAV 200 may continuously uselocalization to update its map of the environment. This continuousmapping process may be referred to as simultaneous localization andmapping (SLAM). Other navigation techniques may also be utilized.

In some embodiments, the navigation module 214 may navigate using atechnique that relies on waypoints. In particular, waypoints are sets ofcoordinates that identify points in physical space. For instance, anair-navigation waypoint may be defined by a certain latitude, longitude,and altitude. Accordingly, navigation module 214 may cause UAV 200 tomove from waypoint to waypoint, in order to ultimately travel to a finaldestination (e.g., a final waypoint in a sequence of waypoints).

In a further aspect, the navigation module 214 and/or other componentsand systems of the UAV 200 may be configured for “localization” to moreprecisely navigate to the scene of a target location. More specifically,it may be desirable in certain situations for a UAV to be within athreshold distance of the target location where a payload 228 is beingdelivered by a UAV (e.g., within a few feet of the target destination).To this end, a UAV may use a two-tiered approach in which it uses amore-general location-determination technique to navigate to a generalarea that is associated with the target location, and then use amore-refined location-determination technique to identify and/ornavigate to the target location within the general area.

For example, the UAV 200 may navigate to the general area of a targetdestination where a payload 228 is being delivered using waypointsand/or map-based navigation. The UAV may then switch to a mode in whichit utilizes a localization process to locate and travel to a morespecific location. For instance, if the UAV 200 is to deliver a payloadto a user's home, the UAV 200 may need to be substantially close to thetarget location in order to avoid delivery of the payload to undesiredareas (e.g., onto a roof, into a pool, onto a neighbor's property,etc.). However, a GPS signal may only get the UAV 200 so far (e.g.,within a block of the user's home). A more preciselocation-determination technique may then be used to find the specifictarget location.

Various types of location-determination techniques may be used toaccomplish localization of the target delivery location once the UAV 200has navigated to the general area of the target delivery location. Forinstance, the UAV 200 may be equipped with one or more sensory systems,such as, for example, ultrasonic sensors 204, infrared sensors (notshown), and/or other sensors, which may provide input that thenavigation module 214 utilizes to navigate autonomously orsemi-autonomously to the specific target location.

As another example, once the UAV 200 reaches the general area of thetarget delivery location (or of a moving subject such as a person ortheir mobile device), the UAV 200 may switch to a “fly-by-wire” modewhere it is controlled, at least in part, by a remote operator, who cannavigate the UAV 200 to the specific target location. To this end,sensory data from the UAV 200 may be sent to the remote operator toassist them in navigating the UAV 200 to the specific location.

As yet another example, the UAV 200 may include a module that is able tosignal to a passer-by for assistance in either reaching the specifictarget delivery location; for example, the UAV 200 may display a visualmessage requesting such assistance in a graphic display, play an audiomessage or tone through speakers to indicate the need for suchassistance, among other possibilities. Such a visual or audio messagemight indicate that assistance is needed in delivering the UAV 200 to aparticular person or a particular location, and might provideinformation to assist the passer-by in delivering the UAV 200 to theperson or location (e.g., a description or picture of the person orlocation, and/or the person or location's name), among otherpossibilities. Such a feature can be useful in a scenario in which theUAV is unable to use sensory functions or another location-determinationtechnique to reach the specific target location. However, this featureis not limited to such scenarios.

In some embodiments, once the UAV 200 arrives at the general area of atarget delivery location, the UAV 200 may utilize a beacon from a user'sremote device (e.g., the user's mobile phone) to locate the person. Sucha beacon may take various forms. As an example, consider the scenariowhere a remote device, such as the mobile phone of a person whorequested a UAV delivery, is able to send out directional signals (e.g.,via an RF signal, a light signal and/or an audio signal). In thisscenario, the UAV 200 may be configured to navigate by “sourcing” suchdirectional signals—in other words, by determining where the signal isstrongest and navigating accordingly. As another example, a mobiledevice can emit a frequency, either in the human range or outside thehuman range, and the UAV 200 can listen for that frequency and navigateaccordingly. As a related example, if the UAV 200 is listening forspoken commands, then the UAV 200 could utilize spoken statements, suchas “I'm over here!” to source the specific location of the personrequesting delivery of a payload.

In an alternative arrangement, a navigation module may be implemented ata remote computing device, which communicates wirelessly with the UAV200. The remote computing device may receive data indicating theoperational state of the UAV 200, sensor data from the UAV 200 thatallows it to assess the environmental conditions being experienced bythe UAV 200, and/or location information for the UAV 200. Provided withsuch information, the remote computing device may determine altitudinaland/or directional adjustments that should be made by the UAV 200 and/ormay determine how the UAV 200 should adjust its mechanical features(e.g., its rudder(s), elevator(s), aileron(s), and/or the speed of itspropeller(s)) in order to effectuate such movements. The remotecomputing system may then communicate such adjustments to the UAV 200 soit can move in the determined manner.

C. Communication Systems

In a further aspect, the UAV 200 includes one or more communicationsystems 218. The communications systems 218 may include one or morewireless interfaces and/or one or more wireline interfaces, which allowthe UAV 200 to communicate via one or more networks. Such wirelessinterfaces may provide for communication under one or more wirelesscommunication protocols, such as Bluetooth, WiFi (e.g., an IEEE 802.11protocol), Long-Term Evolution (LTE), WiMAX (e.g., an IEEE 802.16standard), a radio-frequency ID (RFID) protocol, near-fieldcommunication (NFC), and/or other wireless communication protocols. Suchwireline interfaces may include an Ethernet interface, a UniversalSerial Bus (USB) interface, or similar interface to communicate via awire, a twisted pair of wires, a coaxial cable, an optical link, afiber-optic link, or other physical connection to a wireline network.

In some embodiments, a UAV 200 may include communication systems 218that allow for both short-range communication and long-rangecommunication. For example, the UAV 200 may be configured forshort-range communications using Bluetooth and for long-rangecommunications under a CDMA protocol. In such an embodiment, the UAV 200may be configured to function as a “hot spot;” or in other words, as agateway or proxy between a remote support device and one or more datanetworks, such as a cellular network and/or the Internet. Configured assuch, the UAV 200 may facilitate data communications that the remotesupport device would otherwise be unable to perform by itself.

For example, the UAV 200 may provide a WiFi connection to a remotedevice, and serve as a proxy or gateway to a cellular service provider'sdata network, which the UAV might connect to under an LTE or a 3Gprotocol, for instance. The UAV 200 could also serve as a proxy orgateway to a high-altitude balloon network, a satellite network, or acombination of these networks, among others, which a remote device mightnot be able to otherwise access.

D. Power Systems

In a further aspect, the UAV 200 may include power system(s) 220. Thepower system 220 may include one or more batteries for providing powerto the UAV 200. In one example, the one or more batteries may berechargeable and each battery may be recharged via a wired connectionbetween the battery and a power supply and/or via a wireless chargingsystem, such as an inductive charging system that applies an externaltime-varying magnetic field to an internal battery.

E. Payload Delivery

The UAV 200 may employ various systems and configurations in order totransport and deliver a payload 228. In some implementations, thepayload 228 of a given UAV 200 may include or take the form of a“package” designed to transport various goods to a target deliverylocation. For example, the UAV 200 can include a compartment, in whichan item or items may be transported. Such a package may one or more fooditems, purchased goods, medical items, or any other object(s) having asize and weight suitable to be transported between two locations by theUAV. In other embodiments, a payload 228 may simply be the one or moreitems that are being delivered (e.g., without any package housing theitems).

In some embodiments, the payload 228 may be attached to the UAV andlocated substantially outside of the UAV during some or all of a flightby the UAV. For example, the package may be tethered or otherwisereleasably attached below the UAV during flight to a target location. Inan embodiment where a package carries goods below the UAV, the packagemay include various features that protect its contents from theenvironment, reduce aerodynamic drag on the system, and prevent thecontents of the package from shifting during UAV flight.

For instance, when the payload 228 takes the form of a package fortransporting items, the package may include an outer shell constructedof water-resistant cardboard, plastic, or any other lightweight andwater-resistant material. Further, in order to reduce drag, the packagemay feature smooth surfaces with a pointed front that reduces thefrontal cross-sectional area. Further, the sides of the package maytaper from a wide bottom to a narrow top, which allows the package toserve as a narrow pylon that reduces interference effects on the wing(s)of the UAV. This may move some of the frontal area and volume of thepackage away from the wing(s) of the UAV, thereby preventing thereduction of lift on the wing(s) cause by the package. Yet further, insome embodiments, the outer shell of the package may be constructed froma single sheet of material in order to reduce air gaps or extramaterial, both of which may increase drag on the system. Additionally oralternatively, the package may include a stabilizer to dampen packageflutter. This reduction in flutter may allow the package to have a lessrigid connection to the UAV and may cause the contents of the package toshift less during flight.

In order to deliver the payload, the UAV may include a winch system 221controlled by the tether control module 216 in order to lower thepayload 228 to the ground while the UAV hovers above. As shown in FIG.2, the winch system 221 may include a tether 224, and the tether 224 maybe coupled to the payload 228 by a payload coupling apparatus 226. Thetether 224 may be wound on a spool that is coupled to a motor 222 of theUAV. The motor 222 may take the form of a DC motor (e.g., a servo motor)that can be actively controlled by a speed controller. The tethercontrol module 216 can control the speed controller to cause the motor222 to rotate the spool, thereby unwinding or retracting the tether 224and lowering or raising the payload coupling apparatus 226. In practice,the speed controller may output a desired operating rate (e.g., adesired RPM) for the spool, which may correspond to the speed at whichthe tether 224 and payload 228 should be lowered towards the ground. Themotor 222 may then rotate the spool so that it maintains the desiredoperating rate.

In order to control the motor 222 via the speed controller, the tethercontrol module 216 may receive data from a speed sensor (e.g., anencoder) configured to convert a mechanical position to a representativeanalog or digital signal. In particular, the speed sensor may include arotary encoder that may provide information related to rotary position(and/or rotary movement) of a shaft of the motor or the spool coupled tothe motor, among other possibilities. Moreover, the speed sensor maytake the form of an absolute encoder and/or an incremental encoder,among others. So in an example implementation, as the motor 222 causesrotation of the spool, a rotary encoder may be used to measure thisrotation. In doing so, the rotary encoder may be used to convert arotary position to an analog or digital electronic signal used by thetether control module 216 to determine the amount of rotation of thespool from a fixed reference angle and/or to an analog or digitalelectronic signal that is representative of a new rotary position, amongother options. Other examples are also possible.

Based on the data from the speed sensor, the tether control module 216may determine a rotational speed of the motor 222 and/or the spool andresponsively control the motor 222 (e.g., by increasing or decreasing anelectrical current supplied to the motor 222) to cause the rotationalspeed of the motor 222 to match a desired speed. When adjusting themotor current, the magnitude of the current adjustment may be based on aproportional-integral-derivative (PID) calculation using the determinedand desired speeds of the motor 222. For instance, the magnitude of thecurrent adjustment may be based on a present difference, a pastdifference (based on accumulated error over time), and a futuredifference (based on current rates of change) between the determined anddesired speeds of the spool.

In some embodiments, the tether control module 216 may vary the rate atwhich the tether 224 and payload 228 are lowered to the ground. Forexample, the speed controller may change the desired operating rateaccording to a variable deployment-rate profile and/or in response toother factors in order to change the rate at which the payload 228descends toward the ground. To do so, the tether control module 216 mayadjust an amount of braking or an amount of friction that is applied tothe tether 224. For example, to vary the tether deployment rate, the UAV200 may include friction pads that can apply a variable amount ofpressure to the tether 224. As another example, the UAV 200 can includea motorized braking system that varies the rate at which the spool letsout the tether 224. Such a braking system may take the form of anelectromechanical system in which the motor 222 operates to slow therate at which the spool lets out the tether 224. Further, the motor 222may vary the amount by which it adjusts the speed (e.g., the RPM) of thespool, and thus may vary the deployment rate of the tether 224. Otherexamples are also possible.

In some embodiments, the tether control module 216 may be configured tolimit the motor current supplied to the motor 222 to a maximum value.With such a limit placed on the motor current, there may be situationswhere the motor 222 cannot operate at the desired operate specified bythe speed controller. For instance, as discussed in more detail below,there may be situations where the speed controller specifies a desiredoperating rate at which the motor 222 should retract the tether 224toward the UAV 200, but the motor current may be limited such that alarge enough downward force on the tether 224 would counteract theretracting force of the motor 222 and cause the tether 224 to unwindinstead. And as further discussed below, a limit on the motor currentmay be imposed and/or altered depending on an operational state of theUAV 200.

In some embodiments, the tether control module 216 may be configured todetermine a status of the tether 224 and/or the payload 228 based on theamount of current supplied to the motor 222. For instance, if a downwardforce is applied to the tether 224 (e.g., if the payload 228 is attachedto the tether 224 or if the tether 224 gets snagged on an object whenretracting toward the UAV 200), the tether control module 216 may needto increase the motor current in order to cause the determinedrotational speed of the motor 222 and/or spool to match the desiredspeed. Similarly, when the downward force is removed from the tether 224(e.g., upon delivery of the payload 228 or removal of a tether snag),the tether control module 216 may need to decrease the motor current inorder to cause the determined rotational speed of the motor 222 and/orspool to match the desired speed. As such, the tether control module 216may be configured to monitor the current supplied to the motor 222. Forinstance, the tether control module 216 could determine the motorcurrent based on sensor data received from a current sensor of the motoror a current sensor of the power system 220. In any case, based on thecurrent supplied to the motor 222, determine if the payload 228 isattached to the tether 224, if someone or something is pulling on thetether 224, and/or if the payload coupling apparatus 226 is pressingagainst the UAV 200 after retracting the tether 224. Other examples arepossible as well.

During delivery of the payload 228, the payload coupling apparatus 226can be configured to secure the payload 228 while being lowered from theUAV by the tether 224, and can be further configured to release thepayload 228 upon reaching ground level. The payload coupling apparatus226 can then be retracted to the UAV by reeling in the tether 224 usingthe motor 222.

In some implementations, the payload 228 may be passively released onceit is lowered to the ground. For example, a passive release mechanismmay include one or more swing arms adapted to retract into and extendfrom a housing. An extended swing arm may form a hook on which thepayload 228 may be attached. Upon lowering the release mechanism and thepayload 228 to the ground via a tether, a gravitational force as well asa downward inertial force on the release mechanism may cause the payload228 to detach from the hook allowing the release mechanism to be raisedupwards toward the UAV. The release mechanism may further include aspring mechanism that biases the swing arm to retract into the housingwhen there are no other external forces on the swing arm. For instance,a spring may exert a force on the swing arm that pushes or pulls theswing arm toward the housing such that the swing arm retracts into thehousing once the weight of the payload 228 no longer forces the swingarm to extend from the housing. Retracting the swing arm into thehousing may reduce the likelihood of the release mechanism snagging thepayload 228 or other nearby objects when raising the release mechanismtoward the UAV upon delivery of the payload 228.

Active payload release mechanisms are also possible. For example,sensors such as a barometric pressure based altimeter and/oraccelerometers may help to detect the position of the release mechanism(and the payload) relative to the ground. Data from the sensors can becommunicated back to the UAV and/or a control system over a wirelesslink and used to help in determining when the release mechanism hasreached ground level (e.g., by detecting a measurement with theaccelerometer that is characteristic of ground impact). In otherexamples, the UAV may determine that the payload has reached the groundbased on a weight sensor detecting a threshold low downward force on thetether and/or based on a threshold low measurement of power drawn by thewinch when lowering the payload.

Other systems and techniques for delivering a payload, in addition or inthe alternative to a tethered delivery system are also possible. Forexample, a UAV 200 could include an air-bag drop system or a parachutedrop system. Alternatively, a UAV 200 carrying a payload could simplyland on the ground at a delivery location. Other examples are alsopossible.

IV. ILLUSTRATIVE UAV DEPLOYMENT SYSTEMS

UAV systems may be implemented in order to provide various UAV-relatedservices. In particular, UAVs may be provided at a number of differentlaunch sites that may be in communication with regional and/or centralcontrol systems. Such a distributed UAV system may allow UAVs to bequickly deployed to provide services across a large geographic area(e.g., that is much larger than the flight range of any single UAV). Forexample, UAVs capable of carrying payloads may be distributed at anumber of launch sites across a large geographic area (possibly eventhroughout an entire country, or even worldwide), in order to provideon-demand transport of various items to locations throughout thegeographic area. FIG. 3 is a simplified block diagram illustrating adistributed UAV system 300, according to an example embodiment.

In the illustrative UAV system 300, an access system 302 may allow forinteraction with, control of, and/or utilization of a network of UAVs304. In some embodiments, an access system 302 may be a computing systemthat allows for human-controlled dispatch of UAVs 304. As such, thecontrol system may include or otherwise provide a user interface throughwhich a user can access and/or control the UAVs 304.

In some embodiments, dispatch of the UAVs 304 may additionally oralternatively be accomplished via one or more automated processes. Forinstance, the access system 302 may dispatch one of the UAVs 304 totransport a payload to a target location, and the UAV may autonomouslynavigate to the target location by utilizing various on-board sensors,such as a GPS receiver and/or other various navigational sensors.

Further, the access system 302 may provide for remote operation of aUAV. For instance, the access system 302 may allow an operator tocontrol the flight of a UAV via its user interface. As a specificexample, an operator may use the access system 302 to dispatch a UAV 304to a target location. The UAV 304 may then autonomously navigate to thegeneral area of the target location. At this point, the operator may usethe access system 302 to take control of the UAV 304 and navigate theUAV to the target location (e.g., to a particular person to whom apayload is being transported). Other examples of remote operation of aUAV are also possible.

In an illustrative embodiment, the UAVs 304 may take various forms. Forexample, each of the UAVs 304 may be a UAV such as those illustrated inFIGS. 1A-1E. However, UAV system 300 may also utilize other types ofUAVs without departing from the scope of the invention. In someimplementations, all of the UAVs 304 may be of the same or a similarconfiguration. However, in other implementations, the UAVs 304 mayinclude a number of different types of UAVs. For instance, the UAVs 304may include a number of types of UAVs, with each type of UAV beingconfigured for a different type or types of payload deliverycapabilities.

The UAV system 300 may further include a remote device 306, which maytake various forms. Generally, the remote device 306 may be any devicethrough which a direct or indirect request to dispatch a UAV can bemade. (Note that an indirect request may involve any communication thatmay be responded to by dispatching a UAV, such as requesting a packagedelivery). In an example embodiment, the remote device 306 may be amobile phone, tablet computer, laptop computer, personal computer, orany network-connected computing device. Further, in some instances, theremote device 306 may not be a computing device. As an example, astandard telephone, which allows for communication via plain oldtelephone service (POTS), may serve as the remote device 306. Othertypes of remote devices are also possible.

Further, the remote device 306 may be configured to communicate withaccess system 302 via one or more types of communication network(s) 308.For example, the remote device 306 may communicate with the accesssystem 302 (or a human operator of the access system 302) bycommunicating over a POTS network, a cellular network, and/or a datanetwork such as the Internet. Other types of networks may also beutilized.

In some embodiments, the remote device 306 may be configured to allow auser to request delivery of one or more items to a desired location. Forexample, a user could request UAV delivery of a package to their homevia their mobile phone, tablet, or laptop. As another example, a usercould request dynamic delivery to wherever they are located at the timeof delivery. To provide such dynamic delivery, the UAV system 300 mayreceive location information (e.g., GPS coordinates, etc.) from theuser's mobile phone, or any other device on the user's person, such thata UAV can navigate to the user's location (as indicated by their mobilephone).

In an illustrative arrangement, the central dispatch system 310 may be aserver or group of servers, which is configured to receive dispatchmessages requests and/or dispatch instructions from the access system302. Such dispatch messages may request or instruct the central dispatchsystem 310 to coordinate the deployment of UAVs to various targetlocations. The central dispatch system 310 may be further configured toroute such requests or instructions to one or more local dispatchsystems 312. To provide such functionality, the central dispatch system310 may communicate with the access system 302 via a data network, suchas the Internet or a private network that is established forcommunications between access systems and automated dispatch systems.

In the illustrated configuration, the central dispatch system 310 may beconfigured to coordinate the dispatch of UAVs 304 from a number ofdifferent local dispatch systems 312. As such, the central dispatchsystem 310 may keep track of which UAVs 304 are located at which localdispatch systems 312, which UAVs 304 are currently available fordeployment, and/or which services or operations each of the UAVs 304 isconfigured for (in the event that a UAV fleet includes multiple types ofUAVs configured for different services and/or operations). Additionallyor alternatively, each local dispatch system 312 may be configured totrack which of its associated UAVs 304 are currently available fordeployment and/or are currently in the midst of item transport.

In some cases, when the central dispatch system 310 receives a requestfor UAV-related service (e.g., transport of an item) from the accesssystem 302, the central dispatch system 310 may select a specific UAV304 to dispatch. The central dispatch system 310 may accordinglyinstruct the local dispatch system 312 that is associated with theselected UAV to dispatch the selected UAV. The local dispatch system 312may then operate its associated deployment system 314 to launch theselected UAV. In other cases, the central dispatch system 310 mayforward a request for a UAV-related service to a local dispatch system312 that is near the location where the support is requested and leavethe selection of a particular UAV 304 to the local dispatch system 312.

In an example configuration, the local dispatch system 312 may beimplemented as a computing system at the same location as the deploymentsystem(s) 314 that it controls. For example, the local dispatch system312 may be implemented by a computing system installed at a building,such as a warehouse, where the deployment system(s) 314 and UAV(s) 304that are associated with the particular local dispatch system 312 arealso located. In other embodiments, the local dispatch system 312 may beimplemented at a location that is remote to its associated deploymentsystem(s) 314 and UAV(s) 304.

Numerous variations on and alternatives to the illustrated configurationof the UAV system 300 are possible. For example, in some embodiments, auser of the remote device 306 could request delivery of a packagedirectly from the central dispatch system 310. To do so, an applicationmay be implemented on the remote device 306 that allows the user toprovide information regarding a requested delivery, and generate andsend a data message to request that the UAV system 300 provide thedelivery. In such an embodiment, the central dispatch system 310 mayinclude automated functionality to handle requests that are generated bysuch an application, evaluate such requests, and, if appropriate,coordinate with an appropriate local dispatch system 312 to deploy aUAV.

Further, some or all of the functionality that is attributed herein tothe central dispatch system 310, the local dispatch system(s) 312, theaccess system 302, and/or the deployment system(s) 314 may be combinedin a single system, implemented in a more complex system, and/orredistributed among the central dispatch system 310, the local dispatchsystem(s) 312, the access system 302, and/or the deployment system(s)314 in various ways.

Yet further, while each local dispatch system 312 is shown as having twoassociated deployment systems 314, a given local dispatch system 312 mayalternatively have more or fewer associated deployment systems 314.Similarly, while the central dispatch system 310 is shown as being incommunication with two local dispatch systems 312, the central dispatchsystem 310 may alternatively be in communication with more or fewerlocal dispatch systems 312.

In a further aspect, the deployment systems 314 may take various forms.In general, the deployment systems 314 may take the form of or includesystems for physically launching one or more of the UAVs 304. Suchlaunch systems may include features that provide for an automated UAVlaunch and/or features that allow for a human-assisted UAV launch.Further, the deployment systems 314 may each be configured to launch oneparticular UAV 304, or to launch multiple UAVs 304.

The deployment systems 314 may further be configured to provideadditional functions, including for example, diagnostic-relatedfunctions such as verifying system functionality of the UAV, verifyingfunctionality of devices that are housed within a UAV (e.g., a payloaddelivery apparatus), and/or maintaining devices or other items that arehoused in the UAV (e.g., by monitoring a status of a payload such as itstemperature, weight, etc.).

In some embodiments, the deployment systems 314 and their correspondingUAVs 304 (and possibly associated local dispatch systems 312) may bestrategically distributed throughout an area such as a city. Forexample, the deployment systems 314 may be strategically distributedsuch that each deployment system 314 is proximate to one or more payloadpickup locations (e.g., near a restaurant, store, or warehouse).However, the deployment systems 314 (and possibly the local dispatchsystems 312) may be distributed in other ways, depending upon theparticular implementation. As an additional example, kiosks that allowusers to transport packages via UAVs may be installed in variouslocations. Such kiosks may include UAV launch systems, and may allow auser to provide their package for loading onto a UAV and pay for UAVshipping services, among other possibilities. Other examples are alsopossible.

In a further aspect, the UAV system 300 may include or have access to auser-account database 316. The user-account database 316 may includedata for a number of user accounts, and which are each associated withone or more person. For a given user account, the user-account database316 may include data related to or useful in providing UAV-relatedservices. Typically, the user data associated with each user account isoptionally provided by an associated user and/or is collected with theassociated user's permission.

Further, in some embodiments, a person may be required to register for auser account with the UAV system 300, if they wish to be provided withUAV-related services by the UAVs 304 from UAV system 300. As such, theuser-account database 316 may include authorization information for agiven user account (e.g., a user name and password), and/or otherinformation that may be used to authorize access to a user account.

In some embodiments, a person may associate one or more of their deviceswith their user account, such that they can access the services of UAVsystem 300. For example, when a person uses an associated mobile phone,e.g., to place a call to an operator of the access system 302 or send amessage requesting a UAV-related service to a dispatch system, the phonemay be identified via a unique device identification number, and thecall or message may then be attributed to the associated user account.Other examples are also possible.

V. EXAMPLE SYSTEM AND APPARATUS FOR PAYLOAD DELIVERY

FIGS. 4A, 4B, and 4C show a UAV 400 that includes a payload deliverysystem 410 (could also be referred to as a payload delivery apparatus),according to an example embodiment. As shown, payload delivery system410 for UAV 400 includes a tether 402 coupled to a spool 404, a payloadlatch 406, and a payload 408 coupled to the tether 402 via a payloadcoupling apparatus 412. The payload latch 406 can function toalternately secure payload 408 and release the payload 408 upondelivery. For instance, as shown, the payload latch 406 may take theform of one or more pins that can engage the payload coupling apparatus412 (e.g., by sliding into one or more receiving slots in the payloadcoupling apparatus 412). Inserting the pins of the payload latch 406into the payload coupling apparatus 412 may secure the payload couplingapparatus 412 within a receptacle 414 on the underside of the UAV 400,thereby preventing the payload 408 from being lowered from the UAV 400.In some embodiments, the payload latch 406 may be arranged to engage thespool 404 or the payload 408 rather than the payload coupling apparatus412 in order to prevent the payload 408 from lowering. In otherembodiments, the UAV 400 may not include the payload latch 406, and thepayload delivery apparatus may be coupled directly to the UAV 400.

In some embodiments, the spool 404 can function to unwind the tether 402such that the payload 408 can be lowered to the ground with the tether402 and the payload coupling apparatus 412 from UAV 400. The payload 408may itself be an item for delivery, and may be housed within (orotherwise incorporate) a parcel, container, or other structure that isconfigured to interface with the payload latch 406. In practice, thepayload delivery system 410 of UAV 400 may function to autonomouslylower payload 408 to the ground in a controlled manner to facilitatedelivery of the payload 408 on the ground while the UAV 400 hoversabove.

As shown in FIG. 4A, the payload latch 406 may be in a closed position(e.g., pins engaging the payload coupling apparatus 412) to hold thepayload 408 against or close to the bottom of the UAV 400, or evenpartially or completely inside the UAV 400, during flight from a launchsite to a target location 420. The target location 420 may be a point inspace directly above a desired delivery location. Then, when the UAV 400reaches the target location 420, the UAV's control system (e.g., thetether control module 216 of FIG. 2) may toggle the payload latch 406 toan open position (e.g., disengaging the pins from the payload couplingapparatus 412), thereby allowing the payload 408 to be lowered from theUAV 400. The control system may further operate the spool 404 (e.g., bycontrolling the motor 222 of FIG. 2) such that the payload 408, securedto the tether 402 by a payload coupling apparatus 412, is lowered to theground, as shown in FIG. 4B.

Once the payload 408 reaches the ground, the control system may continueoperating the spool 404 to lower the tether 402, causing over-run of thetether 402. During over-run of the tether 402, the payload couplingapparatus 412 may continue to lower as the payload 408 remainsstationary on the ground. The downward momentum and/or gravitationalforces on the payload coupling apparatus 412 may cause the payload 408to detach from the payload coupling apparatus 412 (e.g., by sliding offa hook of the payload coupling apparatus 412). After releasing payload408, the control system may operate the spool 404 to retract the tether402 and the payload coupling apparatus 412 toward the UAV 400. Once thepayload coupling apparatus reaches or nears the UAV 400, the controlsystem may operate the spool 404 to pull the payload coupling apparatus412 into the receptacle 414, and the control system may toggle thepayload latch 406 to the closed position, as shown in FIG. 4C.

In some embodiments, when lowering the payload 408 from the UAV 400, thecontrol system may detect when the payload 408 and/or the payloadcoupling apparatus 412 has been lowered to be at or near the groundbased on an unwound length of the tether 402 from the spool 404. Similartechniques may be used to determine when the payload coupling apparatus412 is at or near the UAV 400 when retracting the tether 402. As notedabove, the UAV 400 may include an encoder for providing data indicativeof the rotation of the spool 404. Based on data from the encoder, thecontrol system may determine how many rotations the spool 404 hasundergone and, based on the number of rotations, determine a length ofthe tether 402 that is unwound from the spool 404. For instance, thecontrol system may determine an unwound length of the tether 402 bymultiplying the number of rotations of the spool 404 by thecircumference of the tether 402 wrapped around the spool 404. In someembodiments, such as when the spool 404 is narrow or when the tether 402has a large diameter, the circumference of the tether 402 on the spool404 may vary as the tether 402 winds or unwinds from the tether, and sothe control system may be configured to account for these variationswhen determining the unwound tether length.

In other embodiments, the control system may use various types of data,and various techniques, to determine when the payload 408 and/or payloadcoupling apparatus 412 have lowered to be at or near the ground.Further, the data that is used to determine when the payload 408 is ator near the ground may be provided by sensors on UAV 400, sensors on thepayload coupling apparatus 412, and/or other data sources that providedata to the control system.

In some embodiments, the control system itself may be situated on thepayload coupling apparatus 412 and/or on the UAV 400. For example, thepayload coupling apparatus 412 may include logic module(s) implementedvia hardware, software, and/or firmware that cause the UAV 400 tofunction as described herein, and the UAV 400 may include logicmodule(s) that communicate with the payload coupling apparatus 412 tocause the UAV 400 to perform functions described herein.

FIG. 5A shows a perspective view of a payload delivery apparatus 500including payload 510, according to an example embodiment. The payloaddelivery apparatus 500 is positioned within a fuselage of a UAV (notshown) and includes a winch 514 powered by motor 512, and a tether 502spooled onto winch 514. The tether 502 is attached to a payload couplingapparatus 800 positioned within a payload coupling apparatus receptacle516 positioned within the fuselage of the UAV (not shown). A payload 510is secured to the payload coupling apparatus 800. In this embodiment atop portion 513 of payload 510 is secured within the fuselage of theUAV. A locking pin 570 is shown extending through handle 511 attached topayload 510 to positively secure the payload beneath the UAV during highspeed flight.

FIG. 5B is a cross-sectional side view of payload delivery apparatus 500and payload 510 shown in FIG. 5A. In this view, the payload couplingapparatus is shown tightly positioned with the payload couplingapparatus receptacle 516. Tether 502 extends from winch 514 and isattached to the top of payload coupling apparatus 800. Top portion 513of payload 510 is shown positioned within the fuselage of the UAV (notshown) along with handle 511.

FIG. 5C is a side view of payload delivery apparatus 500 and payload 510shown in FIGS. 5A and 5B. The top portion 513 of payload 510 is shownpositioned within the fuselage of the UAV. Winch 514 has been used towind in tether 502 to position the payload coupling apparatus withinpayload coupling apparatus receptacle 516. FIGS. 5A-C disclose payload510 taking the shape of an aerodynamic hexagonally-shaped tote, wherethe base and side walls are six-sided hexagons and the tote includesgenerally pointed front and rear surfaces formed at the intersections ofthe side walls and base of the tote providing an aerodynamic shape.

VI. EXAMPLE CAPSULES, RECEPTACLE, AND PACKAGE/TOTE

FIG. 6A is a perspective view of payload coupling apparatus 800,according to an example embodiment. Payload coupling apparatus 800includes tether mounting point 802, and a slot 808 to position a handleof a payload handle in. Lower lip, or hook, 806 is positioned beneathslot 808. Also included is an outer protrusion 804 having helical camsurfaces 804 a and 804 b that are adapted to mate with corresponding cammating surfaces within a payload coupling apparatus receptaclepositioned with a fuselage of a UAV.

FIG. 6B is a side view of payload coupling apparatus 800 shown in FIG.6A. Slot 808 is shown positioned above lower lip, or hook, 806. As shownlower lip or hook 806 has an outer surface 806 a that is undercut suchthat it does not extend as far outwardly as an outer surface above slot805 so that the lower lip or hook 806 will not reengage with the handleof the payload after it has been decoupled, or will not get engaged withpower lines or tree branches during retrieval to the UAV.

FIG. 6C is a front view of payload coupling apparatus 800 shown in FIGS.6A and 6B. Lower lip or hook 806 is shown positioned beneath slot 808that is adapted for securing a handle of a payload.

FIG. 7 is a perspective view of payload coupling apparatus 800 shown inFIGS. 6A-6C, prior to insertion into a payload coupling apparatusreceptacle 516 positioned in the fuselage 550 of a UAV. As notedpreviously payload coupling apparatus 800 includes a slot 808 positionedabove lower lip or hook 806, adapted to receive a handle of a payload.The fuselage 550 of the payload delivery system 500 includes a payloadcoupling apparatus receptacle 516 positioned within the fuselage 550 ofthe UAV. The payload coupling apparatus 800 includes an outer protrusion810 have helical cammed surfaces 810 a and 810 b that meet in a roundedapex. The helical cammed surfaces 810 a and 810 b are adapted to matewith surfaces 530 a and 530 b of an inward protrusion 530 positionedwithin the payload coupling apparatus receptacle 516 positioned withinfuselage 550 of the UAV. Also included is a longitudinal recessedrestraint slot 540 positioned within the fuselage 550 of the UAV that isadapted to receive and restrain a top portion of a payload (not shown).As the payload coupling apparatus 800 is pulled into to the payloadcoupling apparatus receptacle 516, the cammed surfaces 810 a and 810 bof outer protrusion 810 engage with the cammed surfaces 530 a and 530 bwithin the payload coupling apparatus receptacle 516 and the payloadcoupling apparatus 800 is rotated into a desired alignment within thefuselage 550 of the UAV.

FIG. 8 is another perspective view of an opposite side of payloadcoupling apparatus 800 shown in FIGS. 6A-6C, prior to insertion into apayload coupling apparatus receptacle 516 positioned in the fuselage 550of a UAV. As shown, payload coupling apparatus 800 include a lower lipor hook 806. An outer protrusion 804 is shown extending outwardly fromthe payload coupling apparatus having helical cammed surfaces 804 a and804 b adapted to engage and mate with cammed surfaces 530 a and 530 b ofinner protrusion 530 positioned within payload coupling apparatusreceptacle 516 positioned within fuselage 550 of payload delivery system500. It should be noted that the cammed surfaces 804 a and 804 b meet ata sharp apex, which is asymmetrical with the rounded or blunt apex ofcammed surfaces 810 a and 810 b shown in FIG. 7. In this manner, therounded or blunt apex of cammed surfaces 810 a and 810 b preventpossible jamming of the payload coupling apparatus 800 as the cammedsurfaces engage the cammed surfaces 530 a and 530 b positioned withinthe payload coupling apparatus receptacle 516 positioned within fuselage550 of the UAV. In particular, cammed surfaces 804 a and 804 b arepositioned slightly higher than the rounded or blunt apex of cammedsurfaces 810 a and 810 b. As a result, the sharper tip of cammedsurfaces 804 a and 804 b engages the cammed surfaces 530 a and 530 bwithin the payload coupling apparatus receptacle 516 positioned withinthe fuselage 550 of payload delivery system 500, thereby initiatingrotation of the payload coupling apparatus 800 slightly before therounded or blunt apex of cammed surfaces 810 a and 810 b engage thecorresponding cammed surfaces within the payload coupling apparatusreceptacle 516. In this manner, the case where both apexes (or tips) ofthe cammed surfaces on the payload coupling apparatus end up on the sameside of the receiving cams within the payload coupling apparatusreceptacle is prevented. This scenario results in a prevention of thejamming of the payload coupling apparatus within the receptacle.

FIG. 9 shows a perspective view of a recessed restraint slot and payloadcoupling apparatus receptacle positioned in a fuselage of a UAV. Inparticular, payload delivery system 500 includes a fuselage 550 having apayload coupling apparatus receptacle 516 therein that includes inwardprotrusion 530 having cammed surfaces 530 a and 530 b that are adaptedto mate with corresponding cammed surfaces on a payload couplingapparatus (not shown). Also included is a longitudinally extendingrecessed restrained slot 540 into which a top portion of a payload isadapted to be positioned and secured within the fuselage 550.

FIG. 10A shows a side view of a payload delivery apparatus 500 with ahandle 511 of payload 510 secured within a payload coupling apparatus800 as the payload 510 moves downwardly prior to touching down fordelivery. Prior to payload touchdown, the handle 511 of payload 510includes a hole 513 through which a lower lip or hook of payloadcoupling apparatus 800 extends. The handle sits within a slot of thepayload coupling apparatus 800 that is suspended from tether 502 ofpayload delivery system 500 during descent of the payload 510 to alanding site.

FIG. 10B shows a side view of payload delivery apparatus 500 afterpayload 510 has landed on the ground showing payload coupling apparatus800 decoupled from handle 511 of payload 510. Once the payload 510touches the ground, the payload coupling apparatus 800 continues to movedownwardly (as the winch further unwinds) through inertia or gravity anddecouples the lower lip or hook 808 of the payload coupling apparatus800 from handle 511 of payload 510. The payload coupling apparatus 800remains suspended from tether 502, and can be winched back up to thepayload coupling receptacle of the UAV.

FIG. 10C shows a side view of payload delivery apparatus 500 withpayload coupling apparatus 800 moving away from handle 511 of payload510. Here the payload coupling apparatus 800 is completely separatedfrom the hole 513 of handle 511 of payload 510. Tether 502 may be usedto winch the payload coupling apparatus back to the payload couplingapparatus receptacle positioned in the fuselage of the UAV.

FIG. 11 is a side view of handle 511 of payload 510. The handle 511includes a hole 513 through which the lower lip or hook of a payloadcoupling apparatus extends through to suspend the payload duringdelivery. The handle 511 includes a lower portion 515 that is secured tothe top portion of a payload. Also included are holes 514 and 516through which locking pins positioned within the fuselage of a UAV mayextend to secure the handle and payload in a secure position during highspeed forward flight to a delivery location. The handle may be comprisedof a thin, flexible plastic material that is flexible and providessufficient strength to suspend the payload beneath a UAV during forwardflight to a delivery site, and during delivery and/or retrieval of apayload. In practice, the handle may be bent to position the handlewithin a slot of a payload coupling apparatus. The handle 511 also hassufficient strength to withstand the torque during rotation of thepayload coupling apparatus into the desired orientation within thepayload coupling apparatus receptacle, and rotation of the top portionof the payload into position with the recessed restraint slot.

FIG. 12 shows a pair of locking pins 570, 572 extending through holes514 and 516 in handle 511 of payload 510 to secure the handle 511 andtop portion of payload 510 within the fuselage of a UAV. In this manner,the handle 511 and payload 510 may be secured within the fuselage of aUAV. In this embodiment, the locking pins 570 and 572 have a conicalshape so that they pull the package up slightly or at least remove anydownward slack present. In some embodiments the locking pins 570 and 572may completely plug the holes 514 and 516 of the handle 511 of payload510, to provide a very secure attachment of the handle and top portionof the payload within the fuselage of the UAV. Although preferably thelocking pins are conical, in other applications they may have othergeometries, such as a cylindrical geometry.

FIG. 13A is a perspective view of payload coupling apparatus 900 priorto having a handle of a payload positioned within slot 920 of payloadcoupling apparatus 900. Payload coupling apparatus 900 has a tether slot906 on inner surface 904 of portion 914 into which a tether 902 isinserted. Also included is a pair of upwardly extending fingers 908 and910 having a slot 912 positioned therebetween. A handle of a payload maybe inserted into the slot 920 of payload coupling apparatus 900positioned between upwardly extending fingers 908 and 910 and innersurface 904.

FIG. 13B is a perspective view of payload coupling apparatus 900 afterdelivering a payload and decoupling the payload coupling apparatus 900from a handle of a payload. In this embodiment, the upper portion ofportion 914 is weighted such that when the payload coupling apparatus900 is decoupled from the handle of the payload, the payload couplingapparatus 900 rotates 180 degrees such that the fingers 908 and 910 aredownwardly extending, thereby preventing the slot 920 from reengagingwith the handle of the payload, or engaging with tree branches or wiresduring retrieval to the fuselage of the UAV. During rotation followingdecoupling, the tether 902 is pulled from the tether slot 906 (shown inFIG. 13A) and passes through slot 912 between fingers 908 and 910 suchthat the payload coupling apparatus 900 is suspended from tether 902.

FIGS. 14A-E provide various views of payload coupling apparatus 900shown in FIGS. 13A and 13B. As shown in FIGS. 14A-E, the payloadcoupling apparatus 900 includes a slot 920 positioned between upwardlyextending fingers 908 and 910 and inner surface 904. A tether slot 906is positioned in inner surface 904. A slot 912 also extends betweenupwardly extending fingers 908 and 910. A tether attachment point 922 ispositioned on a bottom of the payload coupling apparatus 900. The tetherslot 906 extends from tether attachment point 922 to the top of innersurface 904. Upper portion 914 of payload coupling apparatus 914 isweighted such that upon payload landing, the payload coupling apparatusis automatically decoupled from the handle of the payload, and theweighted upper portion 914 causes the payload coupling apparatus 900 torotate downwardly 180 degrees. During this period of rotation, a tetheris pulled free from tether slot 906 and the payload coupling apparatusis suspended from the UAV via the tether attached to tether attachmentpoint 922 with fingers 908 and 910 pointing downwardly. As a result, thefingers 908 and 910 are prevented from reengaging the handle of thepayload when retrieved to the UAV, and also prevented from engaging treebranches or power lines during retrieval to the UAV. Although not shownin FIGS. 14A-E, the payload coupling apparatus 900 could also includecammed surfaces as shown in payload coupling apparatus 800 that engagewith mating cams positioned within a payload coupling apparatusreceptacle in the fuselage of a UAV to orient the payload couplingapparatus in a desired orientation within the payload coupling apparatusreceptacle.

Payload coupling apparatus 900 also advantageously is a solid statedesign that includes no moving parts, thereby reducing the complexityand cost of the payload coupling apparatus and eliminating moving partsthat can possibly fail. A more reliable payload coupling apparatus isthereby provided.

FIGS. 15A-E provide various views of payload coupling apparatus 1000. Inthis embodiment, payload coupling apparatus 1000 has a generallyspherical shape. A slot 1020 is positioned between outer lip or hook1010 and rounded portion 1014. The slot 1020 is adapted to receive ahandle of a payload. A tether attachment point 1022 is positioned onrounded portion 1014. A tether slot 1006 extends from tether attachmentpoint 1022 to slot 1020 and is adapted to receive and hold a tether.Rounded portion 1014 or portion 1010 may be weighted such that when apayload touches the ground, the handle of the payload is decoupled fromthe slot of payload coupling apparatus 1000. During decoupling from thehandle of the payload, the weighted, rounded portion 1010 tips forwardand rotates 90 degrees such that the payload coupling apparatus 1000 issuspended from the end of a tether attached to tether attachment point1022. In this manner, the slot 1020 no longer faces upwardly andprevents the payload coupling apparatus 1000 from reengaging with thehandle of the payload during retrieval to a UAV, and also prevents thepayload coupling apparatus from engaging tree branches or power lines.

As with payload coupling apparatuses 800 and 900 described above,payload coupling apparatus 1000 also advantageously is a solid statedesign that includes no moving parts, thereby reducing the complexityand cost of the payload coupling apparatus and eliminating moving partsthat can possibly fail. A more reliable payload coupling apparatus isthereby provided.

FIGS. 16A-D shows various views of payload coupling apparatus 800′ whichis a variation of payload coupling apparatus 800 described above.Payload coupling apparatus 800′ includes the same exterior features aspayload coupling apparatus 800. However, in payload coupling apparatus800′, a lower lip or hook 806′ includes an upwardly extending shank 806a′ that extends within shank cavity 817 in housing 812 of the payloadcoupling apparatus 800′. An end of a tether extends through housing 812and is attached to the end of shank 806 a′. The housing 812 may be movedupwardly into a position shown in FIGS. 16A and 16C thereby opening slot808 between lower lip or hook 806′ and housing 812 and allowing forplacement of a handle of a payload within slot 808.

Once the handle of the payload is positioned within slot 808, thehousing 812 moves downwardly via gravity to close the slot 808 andsecure the handle of the payload between lower lip or hook 806′ andhousing 812, as shown in FIGS. 16B and 16D. Once the payload touchesdown, the payload coupling apparatus 800′ moves downwardly such that thehandle of the payload is removed from the slot 808 and decoupled frompayload coupling apparatus 800′.

In addition, once the handle of the payload is decoupled from thepayload coupling apparatus 800′, gravity forces the housing 817 intoengagement with lower lip or hook 806 a′ such that the slot 808 is inits normally closed position. In this manner, the reengagement with thehandle of the payload during retrieval is prevented, and because theslot 808 is in its normally closed position, engagement with treebranches or power lines is also prevented.

In each of the payload coupling apparatuses 800, 800′, 900, and 1000,the upper and lower ends are rounded, or hemispherically shaped, toprevent the payload coupling apparatus from snagging during descentfrom, or retrieval to, the fuselage of a UAV.

The present embodiments provide a highly integrated winch-based pickupand delivery system for UAVs. A number of significant advantages areprovided. For example, the ability to pick up and deliver packageswithout the need for landing is provided, as the system is able to winchup a package with the aircraft hovering. Although in some locations,infrastructure such as a platform or perch for landing or loading theUAV may be provided, in other location there may be no need forinfrastructure at the merchant or customer location. The advantagesinclude high mission flexibility and potentially little or noinfrastructure installation costs, as well as increased flexibility inpayload geometry.

In addition, the payload delivery system may automatically align the topportion of the payload during winch up, orienting it for minimum dragalong the aircraft's longitudinal axis. This alignment enables highspeed forward flight after pick up. The alignment is accomplishedthrough the shape of the payload hook and receptacle. In the payloadcoupling apparatus 800, the lower lip or hook 806 has cam featuresaround its perimeter which always orient it in a defined direction whenit engages into the cam features inside the receptacle of the fuselageof the UAV. The tips of the cam shapes on both sides of the capsule areasymmetric to prevent jamming in the 90 degree orientation. In thisregard, helical cam surfaces may meet at an apex on one side of thepayload coupling mechanism, and helical cam surfaces may meet at arounded apex on the other side of the payload coupling mechanism. Thehook is specifically designed so that the package hangs in thecenterline of the hook, enabling alignment in both directions from 90degrees.

Payload coupling apparatuses 800, 800′, 900, and 1000 include a hookformed about a slot such that hook also releases the payload passivelyand automatically when the payload touches the ground upon delivery.This is accomplished through the shape and angle of the hook slot andthe corresponding handle on the payload. The hook slides off the handleeasily when the payload touches down due to the mass of the capsule andalso the inertia wanting to continue moving the capsule downward pastthe payload. The end of the hook is designed to be recessed slightlyfrom the body of the capsule, which prevents the hook from accidentallyre-attaching to the handle. After successful release, the hook getswinched back up into the aircraft. All this functionality (packagealignment during pickup and passive release during delivery) is achievedwithout any moving parts in this payload coupling apparatuses 800, 900,and 1000 (referred to as a solid state design). This greatly increasesreliability and reduces cost. The simple design also makes userinteraction very clear and self-explanatory.

VII. TETHER CONTROL DURING PAYLOAD PICKUP

A UAV may be able to pick up and deliver a payload without landing. Insome examples, the UAV may be able to raise and lower a payload coupledto a tether by winding and unwinding the tether while hovering. As such,the UAV may pick up and deliver the payload without requiringinfrastructure to be set up by a merchant or customer, therebyincreasing a flexibility of delivery location and/or payload geometryand decreasing or eliminating costs associated with the manufacture orinstallation of infrastructure. In other examples, the UAV may beconfigured to land on various elevated structures, such as a perch orshelf, and, from its elevated landing position, pick up or deliver thepayload by winding or unwinding the tether.

FIG. 17 shows a method 1700 for tethered pickup of a payload (e.g., apackage) for subsequent delivery to a target location. Method 1700 maybe carried out by a UAV such as those described elsewhere herein. Forexample, method 1700 may be carried out by a control system of a UAVwith a winch system. Further, the winch system may include a tetherdisposed on a spool, a motor operable in a first mode and a second modethat respectively counter and assist unwinding of the tether due togravity (e.g., by driving the spool forward or in reverse), a payloadcoupling apparatus that mechanically couples the tether to a payload,and a payload latch switchable between a closed position that preventsthe payload from being lowered from the UAV and an open position thatallows the payload to be lowered from the UAV.

As shown by block 1702 of method 1700, when the UAV arrives at a pickuplocation (also referred to as a source location), the UAV's controlsystem may open the payload latch, such that the tether and the payloadcoupling apparatus can be lowered toward the ground at the pickuplocation.

At block 1704, the control system operates the motor to unwind apredetermined length of the tether. This unwound length may correspondto an expected payload attachment altitude for the payload couplingapparatus, which is attached to the lower end of the tether. The payloadattachment altitude may be an altitude at which a human, or perhaps arobotic device, may grab the payload coupling apparatus for attachingthe coupling apparatus to a payload. For instance, the payloadattachment altitude may be an altitude less than two meters above groundlevel. Other examples are possible as well.

After unwinding the predetermined length of the tether, the controlsystem may wait for a predetermined payload attachment period, as shownby block 1706. This attachment period allows time for a human, orperhaps a robotic device, to attach a payload (e.g., a package fordelivery) to the payload coupling apparatus. The predetermined payloadattachment period may be a fixed value or may vary based on anoperational state of the UAV.

When the payload attachment period ends, the control system may operatethe winch motor in the second mode for a predetermined attachmentverification period, as shown by block 1708. In particular, the motormay operate so as to pull upwards on the tether during the attachmentverification period in order to hold the tether in place or retract thetether at a certain rate. The motor current required to hold the tetherin place or retract the tether at a certain rate will be greater whenthe payload is attached, due to the added weight of the payload. Assuch, the control system may determine, based at least in part on motorcurrent during the predetermined attachment verification period, whetheror not the payload coupling apparatus is mechanically coupled to thepayload, as shown by block 1710.

In practice, for instance, if the motor current is less than anattachment threshold current, the control system may determine that thepayload has not been attached to the payload coupling apparatus, and mayrepeat the process of lowering the payload (this time by somepredetermined additional length), waiting for a predetermined payloadattachment period, and then pulling upwards on the tether to test forpayload attachment, shown in blocks 1704 to 1710. On the other hand, ifthe motor current is greater than or equal to the attachment thresholdcurrent, and block 1710 results in a determination that the payloadcoupling apparatus is mechanically coupled to the payload, the controlsystem may operate the winch motor to retract the tether and lift theattached payload towards the UAV, as shown by block 1712.

The control system may continue retracting the tether until it sensesthat the payload coupling apparatus is at or near the UAV, at whichpoint it initiates actions to secure the payload for flight to thetarget location. For instance, method 1700 includes functions that maybe used to secure a package and a coupling apparatus in a receptacle ofa UAV, such as in the configurations shown in FIGS. 5A-5C.

More specifically, at block 1714, the control system may determine thatboth: (a) the unwound length of tether is less than a threshold lengthand (b) the motor current is greater than a threshold current. When boththese conditions hold true, this may serve as an indication that thepayload coupling apparatus and/or the payload have reached the UAVreceptacle. In particular, when the calculated unwound length of tetheris at or near zero, this may indicate that the payload couplingapparatus and/or the payload have been lifted all the way to the UAV.Further, when the payload coupling apparatus and/or the payload contactthe UAV's receptacle area, the motor current may increase as the motor'sspeed controller attempts to continue pulling the payload upward. And,by considering both these indications, the control system may avoidfalse positives.

Thus, upon detecting both of the above-described indications, thecontrol system may responsively operate the motor in the first mode topull the payload into, and orient the payload within, the receptacle onthe lower surface of the UAV, as shown by block 1716. In particular, thecontrol system may operate the motor to increase the torque applied tothe tether, such as by increasing the current supplied to the motor to apredetermined value, in order to help ensure that the payload couplingapparatus (and perhaps the payload as well) are firmly seated againstthe corresponding surfaces of the UAV's receptacle, such that thepayload latch (e.g., pins 570 and 572 of FIG. 12) can be closed tosecure the payload for flight to the target location. Accordingly, afterapplying torque to the tether in an upward direction for a predeterminedperiod of time, the control system may close the payload latch, as shownby block 1718. With the payload secured for flight, the UAV may navigateto a target location for delivery.

VIII. TETHER CONTROL DURING PAYLOAD DELIVERY

Once the UAV arrives at the target location for delivery, the UAV'scontrol system may responsively operate in a delivery mode. FIG. 18 is aflow chart illustrating a method 1800 for operation of a UAV in adelivery mode, according to an example embodiment.

More specifically, once the UAV arrives at and is hovering over a targetlocation for tethered delivery, the UAV's control system may operate themotor to unwind the tether according to a predetermined descent profile,as shown by block 1802. The predetermined descent profile may control adescent rate of the payload by specifying a desired rotational speed ofthe motor. For example, the descent profile may specify a constantdescent rate or a variable descent rate for the duration of the payloaddescent.

In some examples, the desired rotational motor speeds specified by thepredetermined descent profile could be based on machine-learned datathat could be inferred from data from prior flights. For example, fordelivery to a particular location, the control system could use adescent profile that was previously used during a previous delivery tothe particular location. Alternatively, if use of the descent profileduring a previous delivery to that particular location or some otherlocation resulted in one or more detected errors (e.g., failure todetach the payload from the tether, damaged payload, etc.), then thecontrol system could alter the descent profile (e.g., by increasing ordecreasing the desired motor speeds during various phases of the payloaddescent) or choose to use a default descent profile instead.

In an example method, the control system may not exert significantcontrol over the descent of the payload until it is closer to theground. For instance, at some point while the tether is unwinding, thecontrol system may determine that the unwound length of the tether isgreater than a threshold length, and responsively operate in apre-touchdown mode, as shown by block 1804. The threshold length maycorrespond to a predetermined near-ground altitude of the payload; e.g.,a height where more control is desirable for the safety of bystandersand/or ground structures, and/or to protect the payload and its contentsfrom damage.

As noted, in the pre-touchdown mode, the control system may pay closeattention to the payload to improve the chances of successful release ofthe payload on the ground. In particular, while operating in thepre-touchdown mode, the control system operates the motor such that thetether continues to unwind according to the predetermined descentprofile, as shown by block 1804 a, while monitoring both motor currentand motor speed, as shown by block 1804 b. The motor current may becompared to a predetermined payload-uncoupling current to detect whenthe motor current is less than the predetermined payload-uncouplingcurrent. Additionally, the motor speed may be compared to apredetermined payload-uncoupling speed to detect when the motor speed isless than the predetermined payload-uncoupling speed, as shown by block1804 c. When both the motor current is less than a predeterminedpayload-uncoupling current and the motor speed is less than apredetermined payload-uncoupling speed, the control system responsivelyswitches to operation in a possible-touchdown mode.

The possible-touchdown mode may be implemented in an effort to verifythat the package has, in fact, reached the ground (or put another way,to help prevent false positive detection of contact with the ground).For instance, while operating in the possible-touchdown mode, thecontrol system may analyze the motor current to verify that the motorcurrent remains below the predetermined payload-uncoupling current for atouchdown-verification period (e.g., perhaps allowing for a small amountof fluctuation during this period), as shown by block 1806. In practice,a Schmitt trigger may be applied to verify that the detected drop inmotor current to below the payload-uncoupling threshold is not theresult of noise or some temporary blockage, and is in fact due to thepayload resting on the ground. Other techniques for verifying touchdownof the payload are also possible.

Once touchdown of the payload is verified, the control system operatesthe motor such that over-run of the tether and payload couplingapparatus occurs, as shown by block 1808. Over-run occurs when thepayload comes to a rest while the tether continues to unwind. Inpractice, for example, the control system may switch the winch motorfrom the first mode to the second mode by, e.g., reversing the directionthe motor and thus the direction of torque applied to the tether by themotor. Thus, the motor may switch from slowing the descent of the tetherto forcing the tether to unwind such that over-run of the tether occurs.The over-run of the tether may in turn lower the payload couplingapparatus below a height where coupling to the payload occurs (andperhaps all the way to the ground). In other embodiments, block 1808 mayinvolve the control system simply turning the motor off, and allowinggravity to pull the payload coupling apparatus down and cause the tetherover-run.

Further, as shown in FIGS. 6A-6C, 10A-10C, and 11, the payload and/orpayload coupling apparatus may have interfacing surfaces such that theinteraction of the payload and payload coupling apparatus duringover-run deflects the payload coupling apparatus to the side of thepayload. As such, the coupling feature of the payload coupling apparatus(e.g., a hook) will no longer be aligned with a corresponding couplingfeature of the payload (e.g., a handle on a tote package). Located assuch, the winch system may retract the tether and payload couplingapparatus to the UAV without the payload coupling apparatus re-couplingto the payload, thereby leaving the package on the ground.

In some examples of method 1800, the control system may be configuredto, prior to opening the payload latch, operating the motor to apply anupward force on the tether. This may allow for the payload latch to beopened more easily, as the payload may be arranged to rest some or allof its weight on the payload latch when the latch is in the closedposition. The weight of the payload may increase the friction againstthe payload latch when attempting to switch the latch to the openposition, so lifting the payload a predetermined amount may reduceoccurrences of the payload latch getting stuck in the closed position.Additionally, after opening the payload latch and before unwinding thetether, the control system may be configured to operate the motor tohold the tether in a substantially constant position. This may allow theweight of the payload to pull the payload downward and against thepayload coupling apparatus, causing the payload to become firmly seatedin a coupling mechanism (e.g., a hook) of the payload couplingapparatus.

IX. USER INTERACTION AND FEEDBACK VIA CONTROL OF TETHER

In practice, a user may interact with the disclosed winch system invarious ways and for various reasons. For instance, the user mayinteract with the winch system to manually couple or decouple a payloadto the tether via the payload coupling apparatus, such as for payloaddelivery purposes or for payload pickup purposes. In doing so, the usermay apply forces directly onto the tether and/or may apply forces to thetether via the payload coupling apparatus, among other possibilities.Moreover, such interaction with the winch system may effectively alsoamounts to an interaction with the UAV itself because the UAV couldadjust its operation based on those forces (e.g., the UAV may engage inflight stabilization that accounts for those forces).

When the user interacts with the disclosed winch system, the user couldencounter various challenges. For example, the user may not know how theinteraction with the winch system may ultimately affect operation of thewinch system and/or operation of the UAV. As a result, the user couldinadvertently damage the UAV and/or the winch system. In anotherexample, the user may not know any future operations that the UAV and/orthe winch system plan to carry out. As a result, the user couldinadvertently stop the UAV and/or the winch system from carrying out aplanned operation. In yet another example, the user may want the UAVand/or the winch system to carry out a certain operation, but may nothave the means to control operation of the UAV or of the winch system.Other examples are possible as well.

To help resolve such challenges, the disclosed winch system may beconfigured to control the tether so as to interact with and providefeedback to a user. Specifically, the UAV's control system may beequipped with the capability to interpret direct or indirect userinteractions with the tether, perhaps carrying out certain operations inresponse to the interpreted interactions. Also, the UAV's control systemmay be equipped with the capability to provide information to the userby manipulating the tether, perhaps doing so in response to a userinteraction with the tether.

FIG. 19 illustrates a method 1900 for facilitating control of the tetherfor purposes of interacting with and/or providing feedback to a user. Asshown by block 1902 of method 1900, the UAV's control system maydetermine one or more operational parameters of a motor for a winchdisposed in an aerial vehicle, the winch including a tether and a spool.Then, the control system may detect, in the one or more operationalparameters, an operational pattern of the motor that is indicative of anintentional user-interaction with the tether, as shown by block 1904 ofmethod 1900. Based on the detected operational pattern of the motor thatis indicative of the intentional user-interaction with the tether, thecontrol system may determine a motor response process, as shown by block1906 of method 1900. And as shown by block 1908 of method 1900, thecontrol system may then operate the motor in accordance with thedetermined motor response process.

i. Determining Operational Parameters of a Motor

As noted above, the UAV's control system may determine one or moreoperational parameters of the motor. In practice, an operationalparameter of the motor may be any measure of the motor's activity.Although certain operational parameters are described herein, otheroperational parameters are also possible without departing from thescope of the present disclosure.

By way of example, an operational parameter of the motor may be currentcharacteristics of the motor, such as a current level being provided toand/or generated by the motor over time or at a particular instance intime, among other possibilities. In another example, an operationalparameter of the motor may be speed characteristics of the motor, suchas a speed of rotation of the motor's transmission assembly over time orat a particular instance in time, among other possibilities. In yetanother example, an operational parameter of the motor may be rotationcharacteristics of the motor, such as an extent of rotation of themotor's transmission assembly over time, among other possibilities.Other examples are possible as well.

Generally, the control system may determine one or more operationalparameters of the motor in various ways. For instance, the controlsystem may receive, from one or more sensors coupled to motor, sensordata indicative of operational parameters. Once the control systemreceives the sensor data, the control system may then use the sensordata to determine and/or evaluate the operational parameters of themotor.

By way of example, a current sensor may be coupled to the motor andconfigured to generate current data indicative of a current level beingprovided to and/or generated by the motor. With this arrangement, thecontrol system may receive current data from the current sensor and mayuse the received current data as basis to determine currentcharacteristics of the motor. For instance, the control system may usethe received current data as basis to determine particular current levelof the motor over a particular time period.

In another example, a speed sensor may be coupled to the motor andconfigured to generate speed data indicative of speed of rotation of themotor's transmission assembly. With this arrangement, the control systemmay receive speed data from the speed sensor and may use the receivedcurrent data as basis to determine speed characteristics of the motor.For instance, the control system may use the received speed data asbasis to determine a particular speed of the motor at a particular pointin time.

In yet another example, an encoder may be coupled to the motor'stransmission assembly and configured to generate position datarepresentative of the transmission assembly's over time. With thisarrangement, the control system may receive position data from theencoder and may use the received position data as basis to determinerotation characteristics of the motor. For instance, the control systemmay use the received position data as basis to determine an extentand/or a direction of the transmission assembly's rotation from a firstpoint in time to a second point in time. Other examples and instancesare possible as well.

FIG. 20 next shows a graph illustrative of example currentcharacteristics 2000 of the motor. As shown, the current characteristics2000 represent the motor's current level over time. In practice, thecurrent level may change over time based on various factors. Forinstance, the current level may change based on torque/force that themotor seeks to provide (e.g., to the tether) and/or based on an externaltorque/force provided to the motor (e.g., via the tether), among otherpossibilities. Other examples are possible as well.

ii. Detecting an Operational Pattern of the Motor that is Indicative ofa User-Interaction

As noted above, the control system may detect, in the one or moreoperational parameters, an operational pattern of the motor that isindicative of an intentional user-interaction with the tether. Inpractice, an operational pattern may be any contiguous and/ornon-contiguous sequence of values of one or more operational parametersover time. Moreover, the control system may use any currently knownand/or future developed signal processing techniques or the like todetect an operational pattern. Nonetheless, an operational pattern couldtake various forms.

In one case, an operational pattern may be a pattern found in a singleoperational parameter. For instance, an operational pattern may be aparticular pattern of current characteristics, such as a particularsequence of current levels being represented by current data over time.In another case, however, an operational pattern may involve patternsrespectively found in two or more operational parameters over the sametime period and/or over different respective time periods. For instance,an operational pattern may be a particular pattern of currentcharacteristics over a first time period as well as a particular patternof speed characteristics over a second time period (e.g., same as ordifferent from the first time period). Other cases are possible as well.

Given the above-described arrangement, the control system detecting anoperational pattern may involve the control system detecting variouspatterns among one or more determined parameters. By way of example (andwithout limitation), the control system detecting an operational patternmay involve the control system detecting any combination of thefollowing: a particular relative change of motor current, a particularrate of change of motor current, a particular motor current value, aparticular sequence of motor current values, a particular relativechange of motor speed, a particular rate of change of motor speed, aparticular motor speed value, a particular sequence of motor speedvalues, a particular relative change of motor rotation, a particularrate of change of motor rotation, a particular motor rotation value,and/or a particular sequence of motor rotation values, among others.

In accordance with the present disclosure, as noted, detecting anoperational pattern may specifically involve detecting an operationalpattern of the motor that is indicative of an intentionaluser-interaction with the tether. More specifically, when a userinteracts with the tether in a particular manner, the motor may exhibita particular operational pattern. As such, established operationalpatterns (e.g., established via manual engineering input) that thecontrol system can detect may each correspond to a respectiveuser-interaction with the tether. In this way, when the control systemdetects a particular operational pattern, the control system mayeffectively detect a particular user-interaction with the tether. Inpractice, the control system may do so simply detecting the operationalpattern and without there necessarily being a logical indication of auser-interaction.

In some cases, however, the control system may maintain or may otherwiserefer to mapping data that maps each of a plurality of operationalpatterns of the motor each with a respective user-interaction. Forexample, the mapping data may map a particular current level patternwith an indication of a user providing a particular downward force onthe tether. In practice, the particular downward force may be a forcethat is applied in a direction substantially perpendicular to a groundsurface and/or may be a force that is applied in a direction that is atanother angle (e.g., 45 degrees) relative to the ground surface (e.g.,such as when a user catches an oscillating tether and then tugs on it atan angle). In another example, the mapping data may map a particularspeed level pattern with an indication of a user moving the tether sideto side at a particular rate. In practice, such indications could eachtake on any feasible forms, such as the form of letters, numbers, and/orlogical Boolean values, among others. Accordingly, when the controlsystem detects a particular operational pattern, the control system mayrefer to the mapping data to determine the user-interaction that isrespectively mapped to that particular operational pattern.

Moreover, different operational patterns may sometimes be indicative ofthe same user-interaction. For this reason, the control system may bearranged to detect a first operational pattern and thus effectivelydetect a particular user-interaction with the tether, and may also bearranged to detect a second operational pattern and thus effectivelydetect the same particular user-interaction with the tether, such as forpurposes of determining a motor response process as further describedbelow. Alternatively, two or more operational patterns in the mappingdata could each be mapped to the same user-interaction, so that thecontrol system detects the same user-interaction when referring toeither one of those operational patterns in the mapping data. Othercases are possible as well.

Yet further, when various detectable operational patterns areestablished, at least some of those established patterns could accountfor various external forces that may be applied to the tether, such asexternal forces other than just those being applied by a user during aninteraction with the tether. In particular, the operational patterns mayaccount for gravity, external forces based on weight of the payloadcoupling apparatus, and/or external forces based on weight of a coupledpayload (e.g., a weight of a package to be shipped), among others. Inthis way, the control system may be able to detect an operationalpattern of the motor that is exhibited when such external forces areapplied in combination with external forces that are based on auser-interaction. Other external forces are possible as well.

In yet a further aspect, in addition to or instead of theabove-mentioned mapping data, the control system may use one or moreother approaches to determine a user-interaction based on an operationalpattern of the motor.

In one case, the control system may carry out signal processing and/oranalysis techniques to determine value(s) and/or trend(s) of a signal(e.g., a signal representative of motor speed values) and to determinethe user-interaction based on those value(s) and/or trend(s) of thesignal. For instance, the control system may evaluate a set ofconditions of a signal so as to determine whether or not all conditionswithin the set are determined to be true. If the control systemdetermines that all conditions of the set are true, the control systemmay determine that the signal corresponds to a particularuser-interaction. Otherwise, the control system may evaluate another setof conditions so as to determine whether or not all conditions withinthat other set are determined to be true, and so on. In an example ofthis approach, the control system may determine whether or not a slopeof the signal is within a particular range of slopes and may determinewhether or not a value of the signal exceeds a particular thresholdvalue within a particular threshold extent of time. And the controlsystem may determine that the signal corresponds to a particularuser-interaction if the control system determines both of theseconditions to be true. Other examples are also possible.

In another case, the control system may carry out probability analysistechniques to determine the user-interaction. For example, the controlsystem may determine that a detected operational pattern does notprecisely match one of the operational patterns of the mapping data andthus may apply probability analysis to determine the operational patternof the mapping data to which the detected operational pattern matcheswith the highest likelihood. For instance, when determining the match,the control system may give a higher weight to a certain portion of thedetected signal/pattern compared to the weight given to other portionsof the detected signal/pattern, thereby applying an additional factor todetermine the matching operational pattern and thus to ultimately theuser-interaction based on the mapping data. Other cases and examples arepossible as well.

FIG. 21 next illustrates an example operational pattern of the motorthat is indicative of a particular user-interaction with the tether. Asshown, the control system may detect a particular current spike 2002 inthe above-described current characteristics 2000. To do so, the controlsystem may detect a particular increase in current level over timefollowed by a particular decrease in current level over time.Additionally or alternatively, the control system may do so by detectinga particular rate of increase in current level over time followed by aparticular rate of decrease of current level over time. In either case,the particular current spike 2002 is shown as being indicative of aparticular user-interaction 2110 involving a particular downward forcebeing applied to a tether 2102.

More specifically, FIG. 21 shows a UAV 2100 that includes winch system2106 with a motor configured to control movement of the tether 2102. Asshown, a user 2108 physically interacts with a payload couplingapparatus 2104 that is coupled to the tether 2102. In doing so, the user2108 applied a downward force to the tether 2102 via the payloadcoupling apparatus 2104, the downward force having a magnitude of “F1”.As such, the particular current spike 2002 is indicative of a userapplying to a tether a downward force having a magnitude of “F1”. Otherexamples are possible as well.

iii. Determining a Motor Response Process

As noted above, the control system may determine a motor responseprocess and do so based on the detected operational pattern of the motorthat is indicative of the intentional user-interaction with the tether.In practice, a particular motor response process may involve one or moreparticular operations by the motor, such as application of one or moreparticular torques onto the tether for instance. Moreover, a motorresponse process may be arranged so as to cause the winch system tointeract with the user via the tether and/or to provide feedback to theuser via the tether, among other possibilities.

In accordance with the present disclosure, the control system maydetermine the motor response process in various ways. In one case, thecontrol system may have stored thereon or may otherwise be configured torefer to mapping data that maps a plurality of operational patterns eachwith a respective motor response process. For instance, the mapping datamay map a particular sequence of speed levels with a motor responseprocess involving the motor applying one or more particular torques towind the tether. As such, the control system may determine the motorresponse process by referring to the mapping data to determine therespective motor response process that is mapped to the detectedoperational pattern of the motor.

In another case, the control system may actually determine theparticular user-interaction with the tether that is indicated by thedetected operational pattern of the motor, such as by referring to theabove-described mapping data that maps various operational patternsrespectively to various respective user-interactions. And the controlsystem may then use the determined particular user-interaction as basisfor determining the motor response process.

More specifically, the control system may have stored thereon or mayotherwise be configured to refer to mapping data that maps a pluralityof user-interactions each with a respective motor response process. Forinstance, the mapping data may map a particular side to side movement ofthe tether by a user with a response process involving application of aparticular torque to unwind the tether for a particular duration. Assuch, the control system may determine the motor response process byreferring to the mapping data to determine the respective motor responseprocess that is mapped to the particular user-interaction, which wasoriginally determined based on the above-described mapping data thatmaps various operational patterns to various respectiveuser-interactions. Other cases are also possible.

In a further aspect, in addition to or instead of mapping data, thecontrol system may use one or more other approaches to determine a motorresponse process.

In one case, the control system may carry out signal processing and/oranalysis techniques to determine value(s) and/or trend(s) of a signal(e.g., a signal representative of motor speed values) and to determinethe motor response process based on those value(s) and/or trend(s) ofthe signal. For instance, the control system may evaluate a set ofconditions of a signal so as to determine whether or not all conditionswithin the set are determined to be true. If the control systemdetermines that all conditions of the set are true, the control systemmay determine that the signal corresponds to a particular motor responseprocess. Otherwise, the control system may evaluate another set ofconditions so as to determine whether or not all conditions within thatother set are determined to be true, and so on. In an example of thisapproach, the control system may determine whether or not the signalincludes an inflection point and may determine whether or not a value ofa local maxima of the signal exceeds a particular threshold value. Andthe control system may determine that the signal corresponds to aparticular motor response process if the control system determines bothof these conditions to be true. Other examples are also possible.

In another case, the control system may carry out probability analysistechniques to determine the motor response process. For example, thecontrol system may determine that a detected operational pattern doesnot precisely match one of the operational patterns of the mapping dataand thus may apply probability analysis to determine the operationalpattern of the mapping data to which the detected operational patternmatches with the highest likelihood. For instance, when determining thematch, the control system may determine a state of the environmentand/or of the UAV during which the operational pattern is detected, andmay use the state of the environment and/or of the UAV as an additionalweighted factor for determining the matching operational pattern. Inthis way, once the control system determines the matching operationalpattern using the the probability analysis, the control system may thendetermine the motor response process based on the mapping data. Othercases and examples are also possible.

In a system arranged as described above, the motor response process mayinvolve various motor response operations, some of which are describedbelow. In practice, the control system may determine the motor responseprocess to include a single such motor response operation or anyfeasible combination of these motor response operations. Assuming two ormore motor response operations are determined to be carried out,determining the motor response process may also involve determining anorder for carrying out motor response operations (e.g., with some motorresponse operations possibly being repeated at various points throughoutthe order) and/or a respective duration for applying each motor responseoperation, among other possibilities. Generally, such an order and/ordurations may be determined based on various factors, such as based onthe detected operational pattern of the motor for instance.Alternatively, such an order and/or durations may be predetermined inaccordance with established mapping data.

In either case, various possible motor response operations are describedbelow. Although certain motor response operations are described, othermotor response operations are possible as well without departing fromthe scope of the present disclosure.

In one example, a motor response operation may involve a particularcountering operation that counters unwinding of the tether due to atleast one external force applied to the tether. As part of such anoperation, the control system may operate the motor to apply one or moreparticular counteracting torques that each counteract unwinding of thetether, and possibly apply each counteracting torque for a respectiveduration. Specifically, each such counteracting torque may be at amagnitude that is substantially the same as the external force(s) beingapplied and may be in a direction that is effectively opposite todirection in which external force(s) are applied. In this way, thisresponse operation may resist unwinding of the tether due to theexternal force(s) being applied without necessarily causing retractionof the tether back to the UAV. In practice, a user applying an externalforce to the tether may essentially feel that the tether cannot belowered any further. Moreover, as magnitude of such counteractingtorques increases, the tension of the tether may increase as well.

In another example, a motor response operation may involve a particularassistance operation that assists unwinding of the tether due to atleast one external force applied to the tether. As part of such anoperation, the control system may operate the motor to apply one or moreparticular assistive torques that each assist unwinding of the tether,and possibly apply each assistive torque for a respective duration.Specifically, each such assistive torque may be in a direction that iseffectively that same to direction in which external force(s) areapplied, and may be of any feasible magnitude. In this way, theassistive torques may be used in combination with the external force(s)being applied so as to further help unwinding of the tether. Inpractice, a user applying an external force to the tether mayessentially feel that manual unwinding of the tether has been madeeasier due to lesser resistance to the unwinding.

In yet another example, a motor response operation may involve aparticular retracting operation that retracts the tether against atleast one external force applied to the tether. As part of such anoperation, the control system may operate the motor to apply one or moreparticular retracting torques that each retract the tether against theexternal force(s), and possibly apply each retracting torque for arespective duration. Specifically, each such retracting torque may be ata magnitude that is larger than the external force(s) being applied andmay be in a direction that is effectively opposite to direction in whichexternal force(s) are applied. In this way, this response operation mayresist unwinding of the tether due to the external force(s) beingapplied and in fact cause retraction of the tether back to the UAVdespite the external force(s). In practice, a user applying an externalforce to the tether may essentially feel that the tether is pullingagainst the user to an extent that the tether retracts even as thoughthe user applies the external force.

In yet another example, a motor response operation may occur afterapplication of an external force by a user rather than duringapplication of an external force by a user. For instance, a motorresponse operation may involve a tether movement operation that movesthe tether in accordance with a particular tether movement profile afterthe external force is applied onto the tether. In practice, such a motorresponse operation may allow for user feedback/interaction to be carriedout even when a user no longer physically interacts with the tether.

In this regard, the control system could detect an operational patternindicative of a particular user interaction and then determine a motorresponse process that is to be carried out after the particular userinteraction is complete. In particular, the control system may determinethat the particular user interaction is complete by detecting yetanother operational pattern of the motor that indicates so and/or may dothis in other ways. In either case, once the control system determinesthat the particular user interaction is complete, the control systemcould then carry out the determined motor response process that involvesmovement of the tether in accordance with a particular tether movementprofile.

Generally, the particular tether movement profile may take various formsand may be based on the operational pattern indicative of theuser-interaction. For instance, the tether movement profile may simplyinvolve retraction of the tether back to the UAV at a particular rate.In this instance, movement of the tether in accordance with this tethermovement profile may occur based on detecting an operational patternthat is indicative of the user pulling down on the tether severalconsecutive times. Other instances and examples are possible as well.

FIG. 22 next illustrates an example motor response process. As shown,the control system determines that the above-described particularuser-interaction 2110 corresponds to a motor response process 2200.Specifically, the motor response process 2200 involves a counteringoperation that includes application of a countering torque. Thatcountering torque may have a magnitude of “T1” that is substantially thesame as the magnitude “F1” of the downward force being applied by theuser 2108. Also, that countering torque may be in a direction that iseffectively opposite to the direction of the downward force beingapplied by the user 2108. As such, the control system may ultimatelyoperate the motor of the winch system 2106 to apply that counteringtorque as the user 2108 applies the downward force onto the tether.Other examples are also possible.

iv. Operating the Motor in Accordance with the Determined Motor ResponseProcess

As noted above, once a motor response process is determined, the controlsystem may then operate the motor in accordance with the determinedmotor response process, specifically doing so by transmitting to themotor one or more commands that instruct the motor to carry out certainoperations in line with the response process. And as further notedabove, the control system may do so during and/or after auser-interaction, depending on the motor response process that has beendetermined. Moreover, the motor response process that is carried out maylead to various outcomes in addition to the planned interaction/feedbackwith the user.

For example, the motor response process may correspond to one or moretarget tension forces being encountered by the tether. Specifically,each target tension force may be one that is expected to be experiencedby the tether when the motor applies a certain torque in accordance withthe motor response process. As such, the control system operating themotor in accordance with the determined response process may cause oneor more such target tension forces to be encountered by the tether.

In another example, the motor response process may correspond to one ormore target tether movement being encountered by the tether.Specifically, each target tether movement may be one that is expected tobe experienced by the tether when the motor applies a certain torque inaccordance with the motor response process. As such, the control systemoperating the motor in accordance with the determined response processmay cause one or more such target tether movements to be encountered bythe tether (e.g., a wave pulse traveling through the tether). Otherexamples are also possible.

FIG. 23 next illustrates an example motor response process in which thecontrol system operates the motor to control tension of the tether 2102as the user 2108 grasps onto the tether 2102, such as during the processof manually coupling a payload for instance. Assuming that the UAV 2100substantially maintains its physical position in space while hovering,the control system may proportionally (e.g., linearly) increase thetorque of the motor in a winding direction as a downward force providedby the user 2108 increases, and vice versa. In this way, the tension ofthe tether 2102 may increase as the user 2108 pulls the tether 2102further down, and vice versa. Moreover, the control system may beconfigured proportionally increase the torque of the motor up to amaximum torque, thereby saturating the tension of the tether and ideallypreventing the user 2108 from pulling the UAV 2100 down towards theground.

More specifically, at state 2302 of the motor response process, thecontrol system operates the motor to apply a torque having a magnitude“T1” to counteract the magnitude “F1” of the force provided by the user2108, thereby resulting in a first tension force being encountered bythe tether 2102. Then, at state 2304 of the motor response process, thecontrol system operates the motor to apply a torque having a magnitude“T2” that is larger than “T1” and do so to counteract the forcemagnitude “F2” that is larger than “F1”, thereby resulting in the tether2102 encountering a second tension force that is larger than the firsttension force. Finally, at state 2306 of the motor response process, thecontrol system operates the motor to apply a torque having a magnitude“T3” that is yet larger than “T2” and do so to counteract the forcemagnitude “F3” that is yet larger than “F2”, thereby resulting in thetether 2102 encountering a third tension force that is yet larger thanthe second tension force.

FIG. 24 next illustrates an example motor response process in which thecontrol system may operate the motor to vary the amount, and possiblythe direction, of the torque that is applied to the tether 2102 overtime, specifically doing so to enhance user-experience or for otherreasons. For instance, the control system may operate the motor toreplicate the feel of detents or clicks as the user 2108 pulls down onthe tether 2102, and/or to provide vibrational feedback (e.g., a wavepulse) via the tether 2102, among other possibilities.

More specifically, at state 2402 of the motor response process, thecontrol system operates the motor to apply an assistive torque that hasa magnitude “T1” and is in the same direction as the force provided bythe user 2108, thereby assisting the user 2108 with unwinding of thetether 2102. Then, during unwinding of the tether 2102 at state 2404 ofthe motor response process, the control system operates the motor toapply a counteracting torque having a magnitude “T2” to counteract themagnitude “F2” of the force provided by the user 2108, thereby resultingin a feel of a “detent” being experienced by the user 2108. Finally, atstate 2406 of the motor response process, the control system againoperates the motor to apply an assistive torque, so as to continueassisting the user 2108 with unwinding of the tether 2102. Specifically,this further assistive force is shown as having a magnitude “T3” andbeing provided in the same direction as the force (having magnitude“F3”) provided by the user 2108.

FIG. 25 next illustrates an example motor response process in which thecontrol system interprets the user 2108's interaction with the tether2102 to determine that the user 2108's intention is to cause the UAV2100 and/or the motor of the winch system 2106 to carry out certainoperations. Specifically, at state 2502 of the motor response process,the control system detects an operational pattern that indicates thatthe user 2108 pulled down on the tether 2102 at least three consecutivetimes with a force substantially having magnitude of “F1”. Upondetecting such gesture by the user 2108, the control system mayinterpret the gesture as a signal that a payload has been properlydecoupled from the payload coupling apparatus 2104 and thus that the UAV2100 may proceed with further flight to a target destination. Generally,to facilitate such gestures, users could be provided with a manual orthe like listing the various gestures that are interpretable by thedisclosed system.

More specifically, as shown by state 2504 of the motor response process,the control system responds to the gesture by carrying out a motorresponse process that involves operating the motor to apply a torquehaving a magnitude “T2” for purposes of retracting the tether 2102 backto the UAV 2100. Moreover, the control system does so once the user 2108has completed interaction with the tether 2102 and thus no longerapplies external force(s) to the tether 2102. Finally, once the tether2102 has been retracted, the UAV 2100 may then proceed with forwardflight to a target destination, as shown by state 2506. Other examplesare possible as well.

v. Additional Features of User Interaction and Feedback

In a further aspect, the control system could consider other factors asbasis for determining a motor response process. In practice, the controlsystem may consider such factors in addition to or instead ofconsideration of the detected operational pattern of the motor asdescribed above. Moreover, the control system may consider any feasiblecombination of these factors, possibly giving some factors more weightcompared to others.

In one case, the control system may consider a state of the environmentas basis for determining a motor response process. Specifically, thecontrol system may receive, from one or more of the UAV's sensors (e.g.,image capture device), sensor data representative of the UAV's state ofthe environment, such as of obstacles near the UAV, among otherpossibilities. And the control system may then determine the motorresponse process based at least on that sensor data. For example, if thecontrol system detects an obstacle within a threshold distance away fromthe tether, the control system may responsively select a motor responseprocess in which the tether encounters smaller target tether movementsrather than larger target tether movements, thereby attempting to avoidcollision with the obstacle.

In another case, the control system may consider a UAV's state of flightas basis for determining a motor response process. Specifically, thecontrol system may receive, from a flight management system (e.g.,on-board the UAV and/or external to the UAV), flight data representativeof a state of flight of the UAV, which may be the UAV's flight progressalong a planned flight path, among other possibilities. And the controlsystem may then determine the motor response process based at least onthat flight data. For example, if the control system determine that theUAV's flight progress is significantly behind a planned schedule alongthe flight path, the control system may responsively select a motorresponse process in which the motor begins retracting the tether to acertain extent, so as to indicate to a user that that the UAV's flightprogress is significantly behind the planned schedule. Other cases andexamples are possible as well.

In yet a further aspect, the control system may carry out the disclosedmethod 1900 conditioned upon a payload (e.g., the payload couplingapparatus and/or a coupled payload) being at a payload altitude at whicha user-interaction is expected. More specifically, the control systemmay determine a payload altitude of the payload and may make adetermination that the payload altitude is one at which auser-interaction is expected. Once the control system makes thatdetermination, the control system may then responsively carry out themethod 1900, such as when a user-interaction is actually detected forinstance.

Generally, the control system may use various techniques to determinethe payload altitude. In one example, an altitude sensor may be coupledto the payload (e.g., to the payload coupling apparatus) and the controlsensor may receive, from the altitude sensor, altitude data indicativeof the payload altitude. In another example, the control system maydetermine an unwound length of the tether, such as by using techniquesdescribed herein for instance. Also, the control system may determine aflight altitude based on altitude data received from an altitude sensorof the UAV, among other possibilities. Then, the control system may usethe determined unwound tether length of the tether as well as thedetermined flight altitude as basis for determining the payloadaltitude. For example, the control system may subtract the determinedunwound tether length of the tether (e.g., 5 feet) from the determinedflight altitude (e.g., 11 feet above ground) so as to determine thepayload altitude (e.g., 6 feet above ground).

Moreover, the control system may take various approaches for determiningthat the payload altitude is one at which a user-interaction isexpected. For instance, the control system may determine that thepayload altitude is less than a threshold altitude (e.g., establishedvia manual engineering input). In practice, the threshold altitude maybe a height above ground at which users can feasibly reach the payloadand thus interact with the tether. Other instances are possible as well.

In yet a further aspect, the control system may operate the UAV itselfin accordance with a UAV response process, which may involve at least aparticular movement of the UAV. In practice, the particular movementcould take on any feasible forms. For example, the particular movementmay involve side to side movement of the UAV along an axis in physicalspace. In another example, the particular movement may involveinitiation of forward flight along a flight path, as shown by state 2506of FIG. 25 for instance. Other examples are possible as well.

Generally, the control system may operate the UAV in accordance with theUAV response process in addition to or instead of operating the motor inaccordance with a determined motor response process. And if the controlsystem does so in addition to operating the motor in accordance with amotor response process, the control system may operate the motor and theUAV, respectively, to carry out those processes simultaneously and/or atdifferent times. Moreover, the control system may operate the UAV inaccordance with the UAV response process after and/or during auser-interaction.

Yet further, the control system may determine the UAV response processbased on various factors. In doing so, the control system may considerany feasible combination of those factors, possibly giving more weightto some factors compared to others. Nonetheless, various factors arepossible.

In one example, the control system may determine the UAV responseprocess based on a detected operational pattern of the motor. Forinstance, the control system may have stored thereon or may otherwise beconfigured to refer to mapping data that maps a plurality of operationalpatterns each with a respective UAV response process. For instance, themapping data may map a particular sequence of current levels with a UAVresponse process involving the operating the UAV to tilt by a certainextent and in a certain direction. As such, the control system maydetermine the UAV response process by referring to the mapping data todetermine the respective UAV response process that is mapped to thedetected operational pattern of the motor.

In another example, the control system may determine the UAV responseprocess based on a state of the UAV's environment and/or based on theUAV's state of flight. For instance, if the control system determinesthat the UAV's state of flight involves the UAV hovering over a firstlocation on the ground and that the state of the UAV's environmentincludes a user physically pointing to a second location on the ground,then the UAV response process may involve the UAV flying in hover flightso as to end up hovering over the second location, such as for purposesof delivering a payload at the second location for instance. Otherexamples and aspects are possible as well.

It is noted that the above-described features related to userinteraction/feedback are not limited to a situation in which the UAV ishovering and could be carried out in various situations withoutdeparting from the scope of the present disclosure. For example, thevarious features may be carried out in a situation in which the UAV haslanded on a ledge and the tether has been at least partially unwoundsuch that the tether is suspended by the UAV over an edge of the ledge.Other examples are possible as well.

X. POST-DELIVERY TETHER CONTROL

A. Release Verification

As noted above, when a UAV lowers a payload to the ground by controllinga motor to unwind a tether coupled to the payload, the control system ofthe UAV may monitor the current of the motor and/or the rotation of thespool to verify that the payload has reached the ground. The controlsystem may then operate the motor to cause over-run of the tether bycontinuing to unwind the tether from the spool. Once the touchdown ofthe payload is verified and tether over-run is performed, the controlsystem may operate in a release-verification mode in order to verifyseparation of the payload from the payload coupling apparatus, beforebeginning the process of lifting the payload coupling apparatus back tothe UAV.

FIG. 26 is a flow chart illustrating a release verification method 2600,according to an example embodiment. Method 2600 may be initiated uponthe completion of method 1800 (e.g., at the end of the tether over-runperiod), as part of operation in the release-verification mode.

As shown, method 2600 involves the control system operating the motor inthe first mode (where torque is applied to counter the pull of gravityon the tether) for a release-verification period, as shown by block2602. In practice, the control system may apply a speed profile designedfor release verification. The speed profile may be designed so as tolift the specific weight of the payload coupling apparatus a smalldistance during the release-verification period. Thus, if the payloadhas not been released, the motor will draw more current to follow thisspeed profile, than it does when the payload has been properly releasedfrom the payload coupling apparatus. Accordingly, based at least in parton the motor current during the release-verification period, the controlsystem may determine that the payload is separated from the payloadcoupling apparatus, as shown by block 2604. For instance, the controlsystem may determine that the payload is separated from the payloadcoupling apparatus by determining that the motor current during therelease-verification period is below a threshold current for at least athreshold amount of time. And, in response to this determination, thecontrol system may operate the motor to retract the tether, as shown byblock 2606.

On the other hand, if the motor current during the release-verificationperiod is large enough, then the control system may determine that thepayload has not been separated from the payload coupling apparatus, andmay repeat the processes of operating the motor to cause over-run of thetether (this time, perhaps, by some predetermined additional length) andthen pulling upwards on the tether to test for payload separation, shownin blocks 1808 and 2602 to 2606.

B. Tether Retraction Processes

Once the release of the payload has been verified (e.g., by performingmethod 2600), the control system may switch to a retraction mode, inorder to retract the tether to lift the payload coupling apparatus backto the UAV.

In the retraction mode, the ascent of the payload coupling apparatus maybe divided into two phases: an initial ascent and a final ascent phase.

During the initial ascent, the control system may implement apredetermined ascent rate profile, which may be designed with the safetyof bystanders and/or surrounding structures in mind. After the initialascent is complete (e.g., once a certain length of tether has been woundup), the control system may pause the retraction process, e.g., byoperating the motor to maintain a substantially constant length ofunwound tether.

Due to the reduction in weight suspended from the tether (e.g., theweight of the payload coupling apparatus only), the payload couplingapparatus may be more susceptible to swinging back and forth once thepayload is released. Accordingly, during the pause in the retractionprocess, the control system may evaluate whether the payload couplingapparatus is oscillating (e.g., as a pendulum) and/or determine themagnitude of oscillations, and may evaluate whether actions should betaken to dampen the oscillations. After or during such dampingprocesses, the control system may initiate the final ascent of thepayload coupling apparatus, in which the tether retracts fully to pullthe payload coupling apparatus to the UAV, and seat the payload couplingapparatus in the UAV's receptacle for the flight back to a returnlocation.

More details regarding retraction of the tether and payload couplingapparatus after delivery are provided in reference to FIGS. 38A-38Cbelow.

XI. DAMPING OSCILLATIONS OF A PAYLOAD

In practice, the UAV may sometimes encounter situations in which thetether is at least partially unwound and a suspended payload coupled tothe tether is susceptible to oscillations. In one example of thissituation, the UAV may deploy the tether for delivery of a coupledpayload, thereby making the coupled payload susceptible to oscillations.In another example of this situation, the UAV may deploy the tether forpickup of a payload, thereby making the payload coupling apparatus(e.g., considered to be the payload in this case) susceptible tooscillations. In yet another example of this situation, the UAV mayretract the tether following coupling of the payload for pickup, therebymaking the coupled payload susceptible to oscillations. In yet anotherexample of this situation, the UAV may retract the tether followingrelease of the payload after delivery, thereby making the payloadcoupling apparatus (e.g., again considered to be the payload in thiscase) susceptible to oscillations. Other examples are also possible.

In such situations, various factors may cause oscillations of thesuspended payload. In one example, sufficiently strong wind conditionsmay cause the payload to oscillate. In another example, movement of theUAV to maintain its position in hover mode may cause the payload tooscillate. And in yet another example, oscillations of the payload maybe a result of an external force applied by a user to the tether and/orthe payload itself. Other examples are also possible.

Generally, oscillation of the payload may cause the payload to move backand forth in a pendulum-like motion, also referred to as pendularmotion. In practice, the pendular motion of an oscillating payload couldhave various consequences. For example, the pendular motion of anoscillating payload may have undesirable effects on the stability of theUAV, may create difficulties in positioning the payload in a desiredlocation on the ground, may create an undesired movement of the payloadnear the ground, or may create difficulties in seating the payloadcoupling apparatus in the UAV's receptacle, among other problems.

To resolve these problems, the UAV's control system may perform one ormore damping techniques, such as those described below. As noted above,such damping techniques may be performed after delivery of the payload,during a pause in the tether retraction process. However, it should beunderstood that the below described damping techniques could be appliedin other scenarios as well. Further, damping techniques described hereincould be applied in scenarios where the payload is still attached to thepayload coupling apparatus (perhaps with some adjustments to account forthe increased weight suspended from the tether, as compared to when onlythe payload coupling apparatus is attached). More generally, dampingtechniques disclosed herein could apply in any scenario where a tethersuspends a weight from an aerial vehicle.

A. Detection and Evaluation of Payload Oscillations

In an example implementation, a UAV may include one or more sensorsarranged to generate sensor data indicative of oscillations of thepayload coupling apparatus (and/or of the coupled payload) suspendedbelow the UAV. In practice, these sensors may include a current sensorcoupled to the winch motor, a tension sensor on the tether, an inertialmeasurement unit (IMU) on the UAV and/or on the payload couplingapparatus, an image capture device on the UAV, and/or an encoder on thewinch motor, among other possibilities. Accordingly, the UAV's controlsystem may use sensor data from any combination of such sensors so as todetect oscillations of the payload as well as attributes of theoscillations, such as amplitude, frequency, and/or speed ofoscillations, among other options.

In one case, the current sensor may generate data representative ofelectric current characteristics of the motor. The control system mayreceive such current data and may use the current data as basis fordetecting oscillations of the payload as well as for determiningattributes of those detected oscillations. To do so, the control systemcould refer to mapping data or the like that maps various currentcharacteristics each with an indication of payload oscillations and/orwith respective attributes of payload oscillations. For example, aparticular set of current characteristics (e.g., a particular relativechange in current value) may be mapped to an indication that the payloadis oscillating. Also, another particular set of current characteristics(e.g., a particular rate of change in current value) may be mapped to anindication that the payload is oscillating with a particular amplitudeof oscillation.

In another case, the tension sensor may generate tension datarepresentative of tension of the tether. The control system may receivesuch tension data and may use the tension data as basis for detectingoscillations of the payload as well as for determining attributes ofthose detected oscillations. To do so, the control system could refer tomapping data or the like that maps various tether tensioncharacteristics each with an indication of payload oscillations and/orwith respective attributes of payload oscillations. For example, aparticular set of tether tension characteristics (e.g., a particularrelative change in tension) may be mapped to an indication that thepayload is oscillating. Also, another particular set of tether tensioncharacteristics (e.g., a particular rate of change in tension) may bemapped to an indication that the payload is oscillating with aparticular speed.

In yet another case, the IMU may generate movement data indicative ofmovement of the payload relative to the aerial vehicle. The controlsystem may receive such movement data and may use the movement data asbasis for detecting oscillations of the payload as well as fordetermining attributes of those detected oscillations. To do so, thecontrol system could refer to mapping data or the like that maps variouscharacteristics of movement data each with an indication of payloadoscillations and/or with respective attributes of payload oscillations.For example, a particular set of movement data characteristics may bemapped to an indication that the payload is oscillating. Also, anotherparticular set of movement data characteristics (e.g., movement dataindicative of particular force) may be mapped to an indication that thepayload is oscillating with a particular amplitude of oscillation.

In yet another case, the image capture device may be arranged to facethe payload and thus provide image data representative of position ofthe payload relative to the UAV. With this arrangement, the controlsystem may receive the image data and may use any currently known and/orfuture developed image processing techniques to evaluate the image data.In doing so, the control system may use the image data to determineposition of the payload over time. More specifically, the control systemmay detect oscillation of the payload by determining a difference inposition of the payload over time. Moreover, the control system coulduse the image data as basis for determining attributes of detectedoscillations. For example, the control system may determine a differencebetween certain payload positions over time and then determine amplitudeof oscillation based on the determined difference. In another example,the control system may use the image data to determine a rate of changein position of the payload and then determine a speed of oscillationbased on the determined rate of change. Other cases and examples arepossible as well.

Moreover, various attributes of payload oscillations may depend on theextent to which the tether is unwound. For instance, a shorter unwoundtether length may cause the payload to swing with a higher frequencycompared to a frequency with which the payload swings when the unwoundtether length is longer. For this reason, the control system mayconsider unwound tether length as an additional factor when determiningattributes of payload oscillations. For example, after determining thatthe tether is unwound at a particular length, the control system maydetermine positions of the payload over time. Then, the control systemmay refer to mapping data that maps the combination the determinedunwound length of the tether and the determined positions to aparticular amplitude of oscillations and to a particular frequency ofoscillations. Alternatively, the control system may determine suchattributes based on a predetermined formula that inputs variables, suchthe unwound tether length and determined positions, and that outputsdata indicative of one or more of the above-mentioned attributes. Otherexamples are also possible.

In practice, the control system may determine the unwound tether lengthby receiving from the encoder position data representative of theunwound length of the tether. More specifically, the encoder may becoupled to the motor such that, as the motor carries out rotation tounwind and/or wind the tether, the encoder generated data representativeof an angular position and/or motion of the motor (e.g., of atransmission assembly of the motor). As such, the control system mayreceive the data and may use the data as basis for tracking the unwoundlength of the tether. For example, the control system may detect tworevolutions of the motor in a particular direction based on the datafrom the encoder and may determine that those two revolutions correspondto unwinding of the tether by two meters. Other examples are alsopossible.

In a further aspect, the control system may also use the sensor data asbasis for determining the detected oscillations exceed a threshold(e.g., established via manual engineering input). For example, thecontrol system may determine that the sensor data is indicative of aparticular amplitude of the oscillations of the payload, and maydetermine that the particular amplitude is higher than thresholdamplitude. In another example, the control system that the sensor datais indicative of a particular speed of the oscillations of the payload,such as a speed at which the payload swings back and forth while thetether is partially unwound. In this example, the control system maythen determine that this particular speed is higher than a thresholdspeed. In yet another example, the control system that the sensor datais indicative of a particular frequency of the oscillations of thepayload, such as a frequency at which the payload swings back and forthwhile the tether is partially unwound. In this example, the controlsystem may then determine that this particular frequency is higher thana threshold frequency. Other examples are possible as well.

B. Damping During a Tether Retraction Process

FIG. 27 is a flowchart illustrating a method 2700 for initiating adamping routine (could also be referred to herein as a dampingtechnique), according to an example embodiment. Method 2700 may beimplemented by a UAV's control system during a tether retractionprocess. In practice, the tether retraction process may be carried outafter delivery and/or at other times during pick-up and/or delivery.Moreover, although method 2700 is described as being carried out in thecontext of a payload coupling apparatus, method 2700 could also becarried out in the context of a payload coupled to the payload couplingapparatus.

Turning to method 2700, the UAV may initially be operating in a hoverflight mode, as shown by block 2702. For instance, the UAV may hoverover a target or delivery location, or over a source location. Once thepayload is released on the ground, the UAV's control system may switchto a tether retraction mode, as shown by block 2702. While operating inthe tether retraction mode, the control system may perform a dampingroutine to dampen the oscillations of the payload coupling apparatus, asshown by block 2704. Optionally, the control system may do sospecifically in response to determining that detected oscillationsexceed a threshold.

Generally, the damping routine that the control system performs may beany combination of the damping routines described herein. In some cases,however, the control system may perform one or more damping routineother those described herein and do so without departing from the scopeof method 2700.

As noted above, a damping routine, such as that performed at block 2704,may be carried out during a pause in the ascent process (and perhapsduring a pause while lowering the payload coupling apparatus as well).In some embodiments, the control system may wait until the oscillationsare sufficiently dampened before resuming the process of retracting (orlowering) the tether. For example, the control system may pause until itdetermines that the amplitude of the oscillations is less than athreshold amplitude, or possibly even that the payload couplingapparatus is resting in an equilibrium position. In either case, thecontrol system may responsively resume retraction of the tether to liftthe payload coupling apparatus to the UAV. In other embodiments,however, the control system may not wait until the oscillations aresufficiently dampened before resuming the process of retracting (orlowering) the tether. For example, the control system might pause thetether retraction process for a fixed period of time before resuming.Specifically, upon starting performance of the damping routine, thecontrol system may initiate a timer that is arranged to expire after aparticular duration (e.g., established via manual engineering input),and may resume the process of retracting (or lowering) the tether inresponse to detecting expiration of that timer. Other examples are alsopossible.

FIGS. 28A to 28D next collectively illustrate initiation of a dampingroutine during a tether retraction process.

As shown by FIG. 28A, a UAV 2800 includes tether 2802 and a payloadcoupling apparatus 2804 coupled to the tether 2802. Also, a payload 2806is shown as having been delivered by the UAV 2800 at a delivery locationon the ground. Moreover, FIG. 28A shows that the UAV 2800 is hoveringover the delivery location while the UAV's control system operates inthe tether retraction mode to ascent the payload coupling apparatus 2804back to the UAV after delivery of the payload 2806.

As shown by FIG. 28B, while operating in the tether retraction mode, theUAV's control system pauses the ascent of the payload coupling apparatus2804. During the pause, the control system performs a damping routine,as indicated by FIG. 28B. As noted, the damping routine could be any ofthe damping routines described herein, among others. Optionally, asnoted, the control system performs the damping routine in response todetecting that oscillations of the payload coupling apparatus 2804 areat an oscillation amplitude 2808 that is greater than a thresholdamplitude.

As shown by FIG. 28C, while the UAV's control system still pauses ascentof the payload coupling apparatus 2804, the oscillations are shown tohave been dampened due to the damping routine. In one case, during thepause and after carrying out of the damping routine for some timeperiod, the control system detects that oscillations of the payloadcoupling apparatus 2804 are at an oscillation amplitude 2810 that islower than the threshold amplitude. In this way, the control systemdetermines that the oscillations have been sufficiently dampened andresponsively determines that the tether retraction process may resume.In another case, the control system detects expiration of a timerinitiated upon starting performance of the damping routine, anddetermines that the tether retraction process may resume in response todetecting expiration of that timer. As such, in either case, the controlsystem may responsively resume operation in the tether retraction modeto ascent the payload coupling apparatus 2804 back to the UAV 2800 afterdelivery of the payload, as shown by FIG. 28D. Other illustrations arealso possible.

C. Example Damping Techniques

Although several damping techniques are described below, it should beunderstood that other damping techniques and modifications to thedescribed techniques are possible as well without departing from thescope of the present disclosure.

i. Forward Flight to Dampen Oscillations

FIG. 29 is a flowchart illustrating a method 2900 for initiating forwardflight to dampen oscillations. As noted above, the UAV may be configuredto fly in accordance with a hover flight mode and in accordance with aforward flight mode. In hover flight mode, flight dynamics may besimilar to a helicopter. More specifically, lift and thrust may besupplied by rotors that allow the UAV to take off and land verticallyand fly in all directions. In forward flight mode, however, flightdynamics may be similar to an airplane. More specifically, a fixed-wingUAV may be propelled forward by thrust from a jet engine or a propeller,with fixed wings of the UAV providing lifting and allowing the UAV toglide substantially horizontally relative to the ground.

With this arrangement, the UAV may operate in accordance with hoverflight mode, as shown by block 2902. As noted, the UAV may do so duringa process of deploying the tether for payload pickup and/or for payloaddelivery, or may do so during a process of retracting the tether forpayload pickup and/or for payload delivery. Regardless, while the UAV isin the hover flight mode, the UAV's control system may cause the UAV toswitch from the hover flight mode to the forward flight mode, as shownby block 2904.

Optionally, the control system may do so in response to determining thatdetected oscillations exceed a threshold. Also, the payload at issue maybe considered to be a payload (e.g., a package) that is coupled thepayload coupling apparatus or may be considered to be the payloadcoupling apparatus itself, among other possibilities.

More specifically, by switching to the forward flight mode, the movementof the UAV may result in drag on the payload. Generally, drag isconsidered to be an aerodynamic force or friction that opposes orresists an object's motion through the air due to interaction betweenthe object and molecules of the air. So in a forward flight scenario,airflow may result in drag that is directed along a direction oppositeto the direction of the forward flight. Thus, the resulting drag maydampen the detected oscillations of the payload because the airflow mayhelp stabilize the payload.

Furthermore, in some embodiments, when the control system causes the UAVto switch to the forward flight mode, the control system may also directthe UAV to operate in the forward flight mode with certain flightcharacteristics. In practice, these flight characteristics may includeflight speed, flight direction, and/or flight timing, among otherpossibilities. As such, the control system may determine the appropriateflight characteristics based on various factors. And in accordance withthe present disclosure, the control system may determine the appropriateflight characteristics based at least on the detected oscillations ofthe payload and/or based on other factors.

By way of example, the control system may determine an initial flightspeed for the forward flight mode based at least on the detectedoscillations. In practice, the initial flight speed may be a flightspeed to which the UAV initially accelerates immediately after switchingto forward flight mode and one which the UAV ultimately maintains for atleast some time period during the forward flight mode. So in accordancewith the present disclosure, the control system may determine an initialflight speed that is generally higher when amplitude of the detectedoscillations is greater. For instance, the control system may select afirst initial flight speed when the control system detects a firstamplitude of oscillation of the payload and may select a second initialflight speed when the control system detects a second amplitude ofoscillation of the payload, with the first amplitude being higher thanthe second amplitude and the first initial flight speed being higherthan the second initial flight speed. Note that the initial flight speedmay additionally or alternatively depend on mass and/or drag of thepayload, or may simply be predefined via manual engineering input or thelike.

In another example, the control system may determine flight timing forthe forward flight mode based at least on the detected oscillations. Inparticular, determining flight timing may involve determining a time atwhich to initiate the forward flight mode, a duration for which to carryout damping as part of the forward flight mode, and/or a time to end theforward flight mode, among other possibilities. In either case, thecontrol system may consider various factors related to the detectedoscillations as basis for determining the flight timing. For instance,the control system may determine state of the payload swing, such aswhether the payload is at a top of a swing or a bottom of a swing, anduse that determined state of the payload swing as basis for determiningthe flight timing. In another instance, the control system may determinean extent (e.g., amplitude) of payload oscillations and may determinethe flight timing based on the determined extent. Note that the flighttiming may alternatively be predefined via manual engineering input orthe like. Other instances and examples are possible as well.

In a further aspect, the control system may help facilitate the forwardflight damping routine in various situations. In one example situation,the control system may initiate forward flight to dampen oscillationsduring a process of retracting the tether for payload pickup and/or forpayload delivery. In this example situation, the control system couldtechnically initiate the forward flight at any point of the retractionprocess, such as without a pause in the retraction process. Ideally,however, the control system may operate the motor to pause retraction ofthe tether while the detected oscillations exceed the threshold, whichmay allow the control system to initiate the forward flight mode duringthe pause in the retraction process. Then, once the control systemdetects that oscillations of the payload have been sufficiently dampenedby the drag (e.g., that the detected oscillations no longer exceed thethreshold) and/or after a fixed time delay (e.g., in response todetecting expiration of a timer), the control system may then operatethe motor to resume retraction of the tether.

In another example situation, the control system may initiate forwardflight to dampen oscillations during a process of deploying the tetherfor payload pickup and/or for payload delivery. In this examplesituation, the control system could technically initiate the forwardflight at any point of the deployment process, such as without a pausein the deployment process. Ideally, however, the control system mayoperate the motor to pause deployment of the tether while the detectedoscillations exceed the threshold, which may allow the control system toinitiate the forward flight mode during the pause in the deploymentprocess. Then, once the control system detects that oscillations of thepayload have been sufficiently dampened by the drag and/or after a fixedtime delay (e.g., in response to detecting expiration of a timer), thecontrol system may then operate the motor to resume deployment of thetether. Various other example situations are possible as well.

Yet further, when the control system operates the motor to resumedeployment or retraction of the tether, the control system may ideallydo so while the UAV operates in the forward flight mode, but could alsodo so while the UAV operates in the hover flight mode.

For example, once the control system detects that oscillations of thepayload have been sufficiently dampened by the drag and/or after a fixedtime delay, the control system may responsively operate the motor todeploy or retract the tether as the control system also causes the UAVto continue operating in the forward flight mode. Also, in the contextof retraction for instance, the control system may direct the UAV tomaintain a particular forward flight speed (e.g., the determined initialflight speed) as the tether is being retracted. In this way, the controlsystem may ensure safe and steady retraction of the tether. Then, oncethe control system determines that that tether retraction is complete,the control system may then responsively change (e.g., increase) theforward flight speed, if applicable.

Additionally or alternatively, once the tether has been fully retracted,the control system could then cause the UAV to switch from the forwardflight mode back to the hover flight mode. In this regard, after the UAVswitches back to the hover flight mode, the control system may thenoperate the motor to deploy the tether. In this way, the forward flightmay dampen oscillations of the payload and subsequent hover flight mayallow for tether deployment over a particular location, such as forpayload pickup or delivery purposes. Other examples are possible aswell.

In a further aspect, the control system may carry out method 2900conditioned upon the payload being at a safe distance away from the UAV.Generally, the control system may do so to ensure that the payload doesnot collide with the UAV upon initiation of forward flight and/or may doso for other reasons. Nonetheless, the control system may do so invarious ways. For example, the control system may determine the unwoundlength of the tether and may then determine that the unwound length ofthe tether is higher than a threshold length, thereby indicating to thecontrol system that the payload is at a relatively safe distance awayfrom the UAV. In this way, if the control system seeks to carry outmethod 2900, the control system may do so only if the control systemdetermines that the unwound length of the tether is higher than thethreshold length. Other examples are also possible.

FIGS. 30A to 30D collectively illustrate the technique involving forwardflight to dampen oscillations, specifically doing so during a tetherretraction process.

As shown by FIG. 30A, a UAV 3000 includes tether 3002 and a payloadcoupling apparatus 3004 coupled to the tether 3002. Also, a payload 3006is shown as having been delivered by the UAV 3000 at a delivery locationon the ground. Moreover, FIG. 30A shows that the UAV 3000 is hoveringover the delivery location while the UAV's control system operates inthe tether retraction mode to ascent the payload coupling apparatus 3004back to the UAV after delivery of the payload 3006.

As shown by FIG. 30B, while the UAV 3000 is in hover flight mode, theUAV's control system pauses the ascent of the payload coupling apparatus3004. During the pause, the control system may optionally detect that anunwound length 3010 of the tether 3002 is greater than a thresholdlength. Also, the control system may optionally detect that theoscillations of the payload coupling apparatus 3004 are at anoscillation amplitude 3008 that is greater than a threshold amplitude.In this regard, the control system may then responsively performs theforward flight damping routine, as shown by FIG. 30C. In particular,while the UAV's control system still pauses ascent of the payloadcoupling apparatus 3004, the UAV 3000 responsively switches fromoperating in hover flight mode to operating in forward flight mode. Inother cases however, the control system may not detect oscillations andmay simply carry out the forward flight damping routing for a fixedperiod of time (e.g., until detecting expiration of a timer).

As shown by FIG. 30C, by switching to the forward flight mode, themovement of the UAV 3000 results in drag on the payload couplingapparatus 3004, which dampens the oscillations of the payload couplingapparatus 3004. Accordingly, during the pause and after the UAV carriesout forward flight for some time period, the control system detects thatoscillations of the payload coupling apparatus 3004 are at anoscillation amplitude 3012 that is lower than the threshold amplitude.In this way, the control system determines that the oscillations havebeen sufficiently dampened and responsively determines that the tetherretraction process may resume.

As shown by FIG. 30D, in response to determining that the oscillationshave been sufficiently dampened and/or in response to detectingexpiration of a timer, the control system then resumes operation in thetether retraction mode to ascent the payload coupling apparatus 3004back to the UAV 3000 after delivery of the payload. Moreover, thecontrol system is shown to resume operation in the tether retractionmode as the control system continues directing the UAV 3000 to operatein forward flight mode. Other illustrations are also possible.

ii. Reducing an Extent of Flight Stabilization to Dampen Oscillations

In accordance with an example implementation, the UAV may be operable ina position-hold mode in which the UAV substantially maintains a physicalposition in physical space during hover flight. Generally, the UAV maydo so by engaging in one or more flight stabilization techniques (e.g.,vision-based stabilization and/or IMU-based stabilization) during hoverflight, such as stabilization techniques that are currently known and/orthose developed in the future.

Specifically, the UAV may engage in flight stabilization along threedimensions in physical space, so as to resist movement of the UAV alongany one of those three dimensions and thus to help maintain the UAV'sphysical position. In practice, the three dimensions at issue may be theyaw axis of the UAV, the pitch axis of the UAV, and the roll axis of theUAV. Additionally or alternatively, the three dimensions may include anyfeasible translational axis for the UAV (e.g., any axis along whichtranslational movement of the UAV is possible). But the three dimensionscould also take on various other forms without departing from the scopeof the present disclosure.

FIG. 31 is a flowchart illustrating a method 3100 for reducing an extent(e.g., gains) of flight stabilization to dampen oscillations (“go limp”damping technique). As shown by block 3102 of method 3100, the UAV mayoperate in the position-hold mode. Here again, the UAV may do so duringa process of deploying the tether for payload pickup and/or for payloaddelivery, or may do so during a process of retracting the tether forpayload pickup and/or for payload delivery. Regardless, while the UAV isin the position-hold mode, the UAV's control system may reduce an extentof flight stabilization along at least one dimension, as shown by block3104. Optionally, the control system may do so in response todetermining that detected oscillations exceed the above-describedthreshold. Also, as noted, the payload at issue may be considered to bea payload (e.g., a package) that is coupled the payload couplingapparatus or may be considered to be the payload coupling apparatusitself, among other possibilities.

More specifically, the “go limp” damping technique may involve thecontrol system causing the UAV to reduce an extent of flightstabilization along at least one of the above-mentioned threedimensions. By doing so, the UAV may then move along that dimension(e.g., translational movement along the axis) based on application ofexternal forces to the UAV. In practice, these external forces may be aresult of the oscillations of the payload. And as these payloadoscillations cause movement of the UAV along the at least one dimensionat issue, energy may dissipate over time, thereby resulting in dampingof the detected oscillations due to this energy dissipation.

In accordance with the present disclosure, the act of reducing an extentof flight stabilization along the at least one dimension may takevarious forms.

In one case, reducing an extent of flight stabilization along the atleast one dimension may take the form of completely eliminating any formof stabilization along that dimension and thus allowing the UAV to movealong that dimension strictly based on application of external forces tothe UAV. For example, a swinging payload may apply an external force tothe UAV along a particular axis and, due to the UAV reducingstabilization along the particular axis, the UAV may end up moving alongthe particular axis by an amount that is based on a magnitude of thatexternal force. In this way, the swinging payload may essentially dragthe UAV itself along the particular axis. Other examples are possible aswell.

In another case, however, reducing an extent of flight stabilizationalong the at least one dimension may take the form of reducing theextent of stabilization along the at least one dimension by a certainextent. Specifically, the control system may allow the UAV to move alongthe at least one dimension based on application of external forces tothe UAV, but do so only to a certain extent. For example, the UAV mayengage in flight stabilization after detecting some extent of movementof the UAV along the at least one dimension relative to theabove-mentioned physical position. In this way, the control system mayeffectively allow some range of movement of the UAV along the at leastone dimension relative to the physical position (e.g., up to a two metertranslational movement of the UAV along a particular axis in eachdirection), rather than the UAV attempting to maintain the UAV'sphysical position by resisting any movement of the UAV away from thatphysical position.

Moreover, the control system may consider various factors whendetermining the extent to which to reduce stabilization along the atleast one dimension. In an example implementation, the control systemmay use the detected oscillations as basis for determining a targetextent of stabilization. In doing so, the control system may determine alesser target extent of stabilization when the amplitude of the detectedoscillations is greater, thereby allowing for greater movement of theUAV along the at least one dimension so as to help dissipate energy. Anddue to such greater movement of the UAV, the higher amplitudeoscillations may ultimately dampen. Other cases and examples are alsopossible.

Following reduction of flight stabilization along the at least onedimension, the control system may detect that oscillations of thepayload have been sufficiently dampened and/or may detect expiration ofa timer (e.g., initiated at the start of the “go limp” damping routine),and may responsively cause the aerial vehicle to increase an extent offlight stabilization along the at least one dimension. In accordancewith the present disclosure, such increase of flight stabilization couldtake on various forms.

In one example, assuming that the control system caused the UAV tocompletely eliminate any form of stabilization along that dimension, thecontrol system may cause the UAV to completely activate stabilizationalong that dimension in an attempt to fully maintain the UAV's physicalposition. In another example, again assuming that the control systemcaused the UAV to completely eliminate any form of stabilization alongthat dimension, the control system may cause the UAV to increase anextent of stabilization along that dimension by effectively allowingsome range of movement of the UAV along the at least one dimensionrelative to the physical position. In yet another example, assuming thatthe control system caused the UAV to partially reduce the extent ofstabilization along the at least one dimension, the control system maycause the UAV to increase the extent of stabilization along thatdimension. In this example, the control system may cause the UAV toincrease the extent of stabilization (e.g., to the same extent prior tothe reduction), so as to effectively lessen the allowed range ofmovement of the UAV along the at least one dimension relative to thephysical position. Alternatively, the control system may cause the UAVto increase the extent of stabilization so as to completely activatestabilization along that dimension in an attempt to fully maintain theUAV's physical position. Various other examples are possible as well.

In a further aspect, the control system may help facilitate the “golimp” damping technique in various situations. In one example situation,the control system may initiate the “go limp” damping technique during aprocess of retracting the tether for payload pickup and/or for payloaddelivery. In this example situation, the control system couldtechnically initiate the “go limp” damping technique at any point of theretraction process, such as without a pause in the retraction process.Ideally, however, the control system may operate the motor to pauseretraction of the tether while the detected oscillations exceed thethreshold, which may allow the control system to initiate the “go limp”damping technique during the pause in the retraction process. Then, oncethe control system detects that oscillations of the payload have beensufficiently dampened following reduction in the extent of flightstabilization along at least one dimension (e.g., that the detectedoscillations no longer exceed the threshold) and/or after a fixed timedelay (e.g., upon detecting expiration of a timer), the control systemmay then operate the motor to resume retraction of the tether.

In another example situation, the control system may initiate the “golimp” damping technique during a process of deploying the tether forpayload pickup and/or for payload delivery. In this example situation,the control system could technically initiate the “go limp” dampingtechnique at any point of the deployment process, such as without apause in the deployment process. Ideally, however, the control systemmay operate the motor to pause deployment of the tether while thedetected oscillations exceed the threshold, which may allow the controlsystem to initiate the “go limp” damping technique during the pause inthe deployment process. Then, once the control system detects thatoscillations of the payload have been sufficiently dampened followingreduction in the extent of flight stabilization along at least onedimension and/or after a fixed time delay (e.g., upon detectingexpiration of a timer), the control system may then operate the motor toresume deployment of the tether. Various other example situations arepossible as well.

Yet further, when the control system operates the motor to resumedeployment or retraction of the tether, the control system may do sowhile the flight stabilization along the at least one dimension is stillreduced and/or after flight stabilization along at least one dimensionhas been increased. For example, once the control system detects thatoscillations of the payload have been sufficiently dampened and/ordetects expiration of a timer, the control system may responsivelyoperate the motor to deploy or retract the tether as the control systemalso causes the UAV to maintain reduction in the extent of flightstabilization along the at least one dimension. In another example, oncethe control system detects that oscillations of the payload have beensufficiently dampened and/or detects expiration of a timer, the controlsystem may responsively cause the UAV to increase the extent of flightstabilization along the at least one dimension. In this example, afterthe UAV increases the extent of flight stabilization along the at leastone dimension, the control system may then operate the motor to deployor retract the tether. Other examples are possible as well.

FIGS. 32A to 32H next collectively illustrate the “go limp” dampingtechnique, specifically being carried out during a tether retractionprocess.

As shown by FIG. 32A, a UAV 3200 includes tether 3202 and a payloadcoupling apparatus 3204 coupled to the tether 3202. Also, a payload 3206is shown as having been delivered by the UAV 3200 at a delivery locationon the ground. Moreover, FIG. 32A shows that the UAV 3200 is hoveringover the delivery location while the UAV's control system operates inthe tether retraction mode to ascent the payload coupling apparatus 3204back to the UAV after delivery of the payload 3206. In this regard, theUAV 3200 is shown as being in a position-hold mode in which the UAV 3200substantially maintains a physical position “X,Y” in physical spaceduring hover flight.

As shown by FIG. 32B, while operating in the tether retraction mode, theUAV's control system pauses the ascent of the payload coupling apparatus3204. During the pause, the control system optionally detects thatoscillations of the payload coupling apparatus 3204 are at anoscillation amplitude 3208 that is greater than a threshold amplitude.Responsive to detecting oscillations in this manner and/or responsive toinitiating a timer, the control system then performs the above-described“go limp” damping routine. In particular, the control system causes theUAV to reduce an extent of flight stabilization along at least onedimension. By doing so, the UAV then moves along that dimension based onapplication of external forces to the UAV, which may dampen oscillationsdue to energy dissipation. Such movement and energy dissipation isillustrated by FIGS. 32C to 32F.

More specifically, due to reduction in the extent of flightstabilization along the dimension, the swinging payload couplingapparatus 3204 drags the UAV 3200 in a first direction along thedimension to a position that is at a distance D1 away from position“X,Y”, as shown by FIG. 32C. Subsequently, due to continued reduction inthe extent of flight stabilization along the dimension and due to energydissipation, the swinging payload coupling apparatus 3204 drags the UAV3200 in a second direction (e.g., opposite to the first direction) alongthe dimension to a position that is at a lesser distance D2 (e.g.,smaller than D1) away from the physical position “X,Y”, as shown by FIG.32D. Subsequently, again due to continued reduction in the extent offlight stabilization along the dimension and due to further energydissipation, the swinging payload coupling apparatus 3204 drags the UAV3200 in the first direction along the dimension to a position that is atan even lesser distance D3 (e.g., smaller than D2) away from thephysical position “X,Y”, as shown by FIG. 32E. Finally, again due tocontinued reduction in the extent of flight stabilization along thedimension and due to yet further energy dissipation, the swingingpayload coupling apparatus 3204 drags the UAV 3200 in the seconddirection along the dimension to a position that is at an even lesserdistance D4 (e.g., smaller than D3) away from the physical position“X,Y”, as shown by FIG. 32F. In this manner, the UAV 3200 may continuemoving back and forth along the dimension as energy continuesdissipating.

As next shown by FIG. 32G, the oscillations are shown to have beendampened due to the “go limp” damping routine. Optionally, during thepause and after carrying out of the “go limp” damping routine for sometime period, the control system detects that oscillations of the payloadcoupling apparatus 3204 are at an oscillation amplitude 3210 that islower than the threshold amplitude. In practice, the control system maycarry out such detection while flight stabilization is still reducedalong the dimension and/or after the control system increased flightstabilization along the dimension. Nonetheless, the control systemdetermines that the oscillations have been sufficiently dampened and/ordetects expiration of a timer, and responsively determines that thetether retraction process may resume. As such, the control system mayresponsively resume operation in the tether retraction mode to ascentthe payload coupling apparatus 3204 back to the UAV 3200 after deliveryof the payload, as shown by FIG. 32H. Other illustrations are alsopossible.

iii. Unwinding/Winding Tether to Dampen Oscillations

In accordance with an example implementation, the UAV's control systemmay dampen oscillations of the payload by operating the motor to unwindand/or wind the tether, thereby changing tension on the tether. In doingso, the control system may increase and/or decrease the unwound tetherlength and do so at various rates, which may help dissipate energy andthus ultimately dampen the oscillations of the payload. In this manner,the control system is provided with an additional control input thatdoes not necessarily interfere with the other control objectives of thesystem (e.g., does not prevent the vehicle from holding position whilealso damping payload oscillations).

More specifically, the control system may operate the motor to vary aretraction rate of the tether and/or a deployment rate of the tether. Inpractice, the retraction rate may define timing, extent, and/or speed oftether retraction and the deployment rate may define timing, extent,and/or speed of tether deployment. As such, the control system may mayoperate the motor in the first mode to retract the tether at the atleast one target retraction rate (e.g., determined based on detectedoscillations and/or established via manual engineering input).Additionally or alternatively, the control system may operate the motorin the second mode to deploy the tether at the at least one targetdeployment rate (e.g., determined based on detected oscillations and/orestablished via manual engineering input). With this arrangement, thecontrol system could thus use various specific approaches for dampingoscillations via control of the tether at various rates.

For instance, the control system may control the winding and/orunwinding of the tether, or the rate of winding and/or unwinding of thetether to “pump” the payload much like a swing, with tether let out asthe payload moves toward the bottom of the swing and the tether heldfast (or even wound in) as the payload moves towards the tops of theswing. Moreover, a “pumping” frequency, period, and/or phase of thetether may be respectively matched to an oscillation frequency, period,and/or phase of the payload. By doing this, the energy of the swingingpayload may be removed even as the UAV remains substantially stationary.

Furthermore, the extent of “pumping” of the winch may depend on thedistance between the payload and the UAV, which corresponds to theunwound length of the tether. Specifically, when there is large distancebetween the payload and the UAV, the pendular motion of the payload maybe very slow, on the order of ¼ hertz for instance. At this point, theamount of the tether unwound or wound onto the winch during “pumping” ofthe winch may be on the order of meters. But when the payload is closerto the UAV, the pendular motion may speed up to on the order of 1 hertzor more for instance. In this case, the amount of the tether unwound orwound onto the winch during “pumping” may be on the order ofcentimeters.

Yet further, the rate of speed at which the tether is wound or unwoundmay vary from one period of oscillation to the next as the distance ofthe payload to the UAV changes, and may even be varied within a singleperiod of oscillation. For example, the rate of winding or unwinding maybe proportional to the velocity of the payload or the velocity of thepayload squared. Other examples are possible as well.

With this arrangement, the control system may “pump” the winch whileoperating in the tether retraction mode to engage in ascent of thepayload or while operating in the tether deployment mode to engage indescent of the payload. Specifically, during descent of the payload, theoscillations of the payload may be damped by letting tether out at asthe payload approaches the bottom of the swing. Whereas, when thepayload is moving towards the top of the swing, the amount of tetherunwound from the winch could be reduced or stopped, or the tether couldeven be wound in as the payload moves to the tops of the swing. Such“pumping” of the tether may counteract the pendular motion of thepayload to control and damp the oscillations of the payload. Incontrast, during ascent of the payload, the oscillations of the payloadmay be damped by winding the tether in as the payload moves to the topsof the swing. Whereas, when the payload is moving towards the bottom ofthe swing, the tether could be unwound, or stopped, or wound in at areduced rate. Other approaches are possible as well.

iv. UAV Movement to Dampen Oscillations

In accordance with an example implementation, the UAV's control systemmay dampen oscillations of the payload by directing the UAV itself tomove in various ways throughout physical space. With this approach, thecontrol system may direct the UAV to reactively move in a manner thatoffsets, prevents, or reduces movement of the payload during ascentand/or descent of the payload. Although various such movements aredescribed below, other movements are possible as well without departingfrom the scope of the present disclosure.

More specifically, the control system may be operable to determine atarget path of the payload. This target path may be a target path ofascent of the payload during winding of the tether or may be a targetpath of descent of the payload during unwinding of the tether. Forexample, the target path may be substantially perpendicular to theground and may extend from the ground to the UAV. In this way, thecontrol system may effectively plan to maintain the payloadsubstantially beneath the UAV as the payload is being lowered or raised.But oscillations of the payload may cause the payload to move away fromthe target path as the payload is being lowered or raised.

To help solve this problem, as noted, the control system may cause theUAV to move in various ways. Specifically, at a given point in time, thecontrol system may use the detected oscillations of the payload as basisfor determining a position of the payload relative to the target path.Then, based on the determined position of the payload relative to thetarget path, the control system may determine a movement to be performedby the UAV so as to move the payload closer to the target path, and thecontrol system may cause the UAV to perform that determined movement. Assuch, the control system could repeatedly determine such movements asposition of the payload relative to the target path changes over timedue to oscillations, and could repeatedly cause the UAV to perform themovements to help dampen the oscillations.

By way of example, the pendular motion of the payload could becontrolled by moving or translating the UAV horizontally in response tothe motion of the payload, e.g. by attempting to maintain the payloadbeneath the UAV. Oscillations of the payload (e.g., pendulum-likeswinging) would be damped by having the UAV translate (e.g., move backand forth) in such a way that the oscillations are minimized. Forinstance, the control system may determine that a current position ofthe payload is at a particular distance away from the target path andthat the payload is currently moving in a particular direction relativeto the target path. Responsively, the control system may immediatelycause the UAV to horizontally move in the particular direction and do soby an amount that is based on the particular distance, therebyattempting to maintain the payload beneath the UAV. In this manner, thecontrol system may reactively determine horizontal movements that offsethorizontal forces on the payload, and prevent or damp the oscillation ofthe payload. Other examples are possible as well.

D. Selection of Damping Techniques

FIG. 33 is a flowchart illustrating a method 3300 for selecting one ormore damping routines/techniques to help dampen oscillations of thepayload. In practice, the UAV's control system could carry out method3300 while operating in tether retraction mode or while operating intether deployment mode. In accordance with block 3302 of method 3300,while the tether is at least partially unwound, the control system mayselect one or more damping routines from a plurality of availabledamping routines to dampen the oscillations of the payload. And thecontrol system may then perform those selected damping routines, asshown by block 3304.

In accordance with the present disclosure, the control system may selectany one of the above-described damping routines. Specifically, thecontrol system may select any combination of the following routines:forward flight to dampen oscillations, “go limp” technique to dampenoscillations, winding/unwinding of tether to dampen oscillations, and/orUAV movement to dampen oscillations. In practice, however, the controlsystem could also select other damping routines that are not describedherein and then perform such damping routines individually or incombination with any of the above-described damping routines.

Moreover, the control system may select the damping routines based onvarious factors, some of which are described below. In practice, thecontrol system may use any combination of those factors as basis for theselection, perhaps giving certain factors more weight compared toothers. Although example factors are described below, other factors arepossible as well without departing from the scope of the presentdisclosure.

In one case, the control system may select the one or more dampingroutines based on characteristics of detected oscillations, such asbased on amplitude, speed, and/or frequency of the oscillations, amongothers. For instance, the control system may select the one or moredamping routines based on amplitude of the detected oscillations of thepayload. Specifically, the control system may have stored thereon or maybe configured to refer to mapping data or the like that maps each ofvarious amplitudes with a damping routine or with a combination of twoor more damping routines. By way of example, the mapping data may map acertain amplitude range with the “forward flight” damping technique andanother lower amplitude range with the “winding/unwinding of tether”damping technique. In practice, the mapping data may be arranged in thismanner because “forward flight” may generally be more effective withdamping a more severe swinging of the payload. As such, the controlsystem may use sensor data to determine the amplitude of the detectedoscillations and may then refer to the mapping data to determine one ormore damping routines that correspond to the detected amplitude.

In another case, the control system may select the one or more dampingroutines based on an operating mode of the motor. Specifically, thecontrol system may determine whether the motor is operating in the firstmode in which the motor applies torque to the tether in a windingdirection or whether the motor is operating in the second mode in whichthe motor applies torque to the tether in an unwinding direction. Basedat least in part on the determined mode of operation of the motor, thecontrol system may then select one or more damping routines. Forexample, if the motor is operating in the second mode, the controlsystem may select any damping technique other than the forward flightdamping technique, so as to avoid further increase of the unwound tetherlength in preparation for and/or during forward flight.

In yet another case, the control system may select the one or moredamping routines based on an operating mode of the UAV. Specifically,the control system may determine whether the UAV is operating in apayload pickup mode in which the UAV attempts to pick up the payload orwhether the UAV is operating a payload delivery mode in which the UAVattempts to deliver a payload, perhaps respectively determining a stateof payload delivery or of payload pickup. Based at least in part on thedetermined mode of operation of the UAV, the control system may thenselect one or more damping routines. For example, the control system mayselect the forward flight damping technique if the UAV is engaging inpost-delivery tether retraction as part of the payload delivery mode. Inpractice, the control system may do so because the UAV can begin forwardflight to the next destination as soon the payload has been delivered.Whereas, the control system may select the UAV movement dampingtechnique if the UAV is engaging in post-pickup tether retraction aspart of the payload pickup mode, and do so because the UAV movement mayhelp ensure that the picked up payload is frequently located directlybeneath the UAV as the payload ascends towards the UAV.

In yet another case, the control system may select the one or moredamping routing based on a value of the payload. In practice, the valueof the payload may be a price of the payload and/or may be a priority ofthe payload being delivered, among other options. Nonetheless, thecontrol system may determine the value of the payload based on inputprovided by a user and/or by using object recognition technique todetermine the value of the payload based on image data, among otherpossibilities. With this arrangement, the control system may refer tomapping data that maps each of various values with a damping routine orwith a combination of two or more damping routines. For example, themapping data may map higher values with the “go limp” damping techniquesbecause the “go limp” technique may pose minimum risk for damaging ahigher value payload. As such, the control system may refer to themapping data to determine one or more damping routines that correspondto the determined value of the payload.

In yet another case, the control system may select the one or moredamping routines based on a state of an environment in which the UAV islocated. Specifically, the control system may use sensor data or thelike to determine information about the environment in which the UAV islocated, such as about objects in the environment for instance. Withthis arrangement, the control system may then use the information aboutthe environment to select one or more damping routines. For example, ifcontrol system determines that an object is located within a thresholddistance away from the UAV, the control system may select the“unwinding/winding of tether” damping technique so as to avoid anymovement of the UAV resulting from engagement in any of the otherdamping techniques, thereby avoiding collision with the object. Othercases are possible as well.

In a further aspect, when the control system selects one or more dampingroutines, the control system may also determine duration for which tocarry out each selected routine (e.g., a duration for which to set theabove-mentioned timer), if feasible. In practice, the control system maydetermine each such duration based on one or more of the above-describedfactors and/or may determine each such duration in other ways. Forexample, the control system may determine that a selected dampingroutine should be applied for a longer duration when the amplitude ofthe detected oscillations is greater, thereby allowing enough time tosufficiently dampen the oscillations. Alternatively, the control systemmay simply perform a selected damping routine until the control systemdetects that the oscillations have been sufficiently dampened. Otherexamples are also possible.

In yet a further aspect, when the control system selects two or moredamping routines, the control system may also determine an approach forusing these selected damping routines in combination. In practice, thecontrol system may determine that approach based on one or more of theabove-described factors and/or may determine the approach in other ways.Moreover, although example approaches are described below, other exampleapproaches are also possible without departing from the scope of thepresent disclosure.

In one example approach, the control system may determine a sequence inwhich to use the selected damping routines, such as by determining thata first damping routine should be followed by a second damping routine.For instance, the control system may determine that the “go limp”damping technique should be performed followed by performing of the“unwinding/winding of tether” damping technique. In this regard, thecontrol system may determine that the second damping routine shouldbegin immediately following the end of the first damping routine.Alternatively, the control system may determine that the control systemshould wait for a particular time period after performing the firstdamping routine and then perform the second damping routine uponexpiration of the particular time period. In some cases, the controlsystem may use the particular time period to evaluate the detectedoscillation and may decide to move forward with performing the seconddamping routine only if the oscillations haven't been sufficientlydampened.

In another example approach, the control system may determine that thecontrol system should concurrently perform two or more selected dampingroutines. For instance, the control system may determine that thecontrol system should concurrently perform the UAV movement dampingtechnique and the unwinding/winding of tether damping technique. In thisregard, the control system may determine that the control system shouldstart performing the selected damping routines at the same point intime. Alternatively, the control system may determine that the controlsystem should start performing a first damping routine and, in the midstof performing that first damping routine, begin performing a seconddamping routine. Other example approaches and combinations of thedescribed approaches are possible as well.

E. Additional Damping Aspects

Although various damping techniques are described herein as beingcarried out after or responsive to detecting oscillation of a payload,the various damping techniques may be carried out in other situations aswell. For instance, the control system may be configured to carry outone or more damping technique during certain phases of flight and/orduring certain phases of payload pickup and/or delivery, among otherpossibilities. In this instance, the control system may carry out thosedamping techniques without necessarily detecting oscillations of apayload. In this regard, as noted, the control system may carry out thedamping routine for a certain time period, such as by initiating a timerupon start of a damping routine and then ending the damping routine(and/or carrying out other operations, such as resuming tetherretraction) responsive to detecting expiration of that timer. In thismanner, the control system may essentially take preventative actions tominimize any oscillations that might be present.

XII. FAILURE DETECTION AND CORRECTION METHODS A. Failure to ReleasePayload

As described above with respect to methods 1800 and 2600, the UAV mayoperate in a delivery mode to deliver a payload to a target location andsubsequently operate in a release-verification mode to verify that thepayload has separated from the payload coupling apparatus. However,there may be situations in which the payload does not separate from thepayload coupling apparatus upon delivery. For instance, the payloadcoupling apparatus may become snagged on the payload such that when theUAV motor is operated to cause over-run of the tether, the payloadcoupling apparatus remains coupled to the payload rather than loweringand detaching from the payload. Accordingly, the control system maydetect such a situation and responsively take remedial action by causingthe tether to detach from the UAV rather than causing the payload todetach from the payload coupling apparatus.

FIG. 34 is a flow chart illustrating a method 3400 for detaching atether from a UAV. Method 3400 may be carried out by a UAV such as thosedescribed elsewhere herein. For example, method 3400 may be carried outby a control system of a UAV with a winch system. Further, the winchsystem may include a tether disposed on a spool, a motor operable in afirst mode and a second mode that respectively counter and assistunwinding of the tether due to gravity (e.g., by driving the spoolforward or in reverse), a payload coupling apparatus that mechanicallycouples the tether to a payload, and a payload latch switchable betweena closed position that prevents the payload from being lowered from theUAV and an open position that allows the payload to be lowered from theUAV.

As shown by block 3402, method 3400 involves the control system of theUAV operating the motor to unwind the tether and lower the payloadtoward the ground (e.g., by performing method 1800). The control systemmay be configured to detect when the payload contacts the ground andresponsively initiate a tether over-run process to attempt to releasethe payload from the payload coupling apparatus, as shown by block 3404.Tether over-run occurs when the motor continues to unwind the tetherafter the payload has stopped lowering. During tether over-run, thepayload coupling apparatus continues to lower as the tether is unwound,while the payload remains stationary. This can cause the payloadcoupling apparatus to detach from the payload, for instance, when thepayload is resting on a protruding arm or other hook-like mechanism ofthe payload coupling apparatus. As described above with respect tomethod 1800, the control system may detect when the payload contacts theground by monitoring a speed and/or a current of the motor anddetermining that the motor speed and/or motor current is threshold low.As further described above with respect to method 1800, initiating thetether over-run process may involve operating the motor in the secondmode to forward drive the spool in a direction that causes the tether tocontinue to unwind even after the payload has reached the ground.

Typically, carrying out the tether over-run process would cause thepayload coupling apparatus to detach from the payload. However, insituations where the payload does not release from the payload couplingapparatus, the tether over-run process may be repeatable up to apredetermined number of times, as further shown by block 3404.

In practice, once the payload has reached the ground and the controlsystem has carried out a first tether over-run process to attempt toseparate the payload coupling apparatus from the payload, the controlsystem may determine whether the payload coupling apparatus has actuallyseparated from the payload, based on the current of the motor (e.g., byperforming blocks 2602 and 2604 of method 2600). For example, afteroperating the motor to cause tether over-run, the control system mayoperate the motor to begin retracting the tether, and if the payload isstill attached to the payload coupling apparatus, the extra weight ofthe payload may cause the motor to draw more current. Accordingly, thecontrol system may determine that the payload is still attached to thepayload coupling apparatus by detecting that the motor current isthreshold high.

Responsive to making such a determination, the control system may repeatthe processes of lowering the payload to the ground, operating the motorto cause over-run of the tether (this time, perhaps, by somepredetermined additional length), and then pulling upwards on the tetherto test for payload separation, shown in blocks 3402 and 3404. Theseprocesses may be repeated a number of times until the control systemdetermines that the payload has separated from the payload couplingapparatus or until a threshold number of repetitions has occurred, asshown by block 3404.

The control system may track how many times the processes of causingover-run of the tether and testing for payload separation have beencarried out and may determine that these processes have been repeated athreshold number of times without successfully releasing the payloadfrom the payload coupling apparatus, as shown by block 3406. Responsiveto making this determination, the control system may decide to abandonfurther attempts to separate the payload from the payload couplingapparatus and may instead decide to separate the tether from the UAV byoperating the motor to allow the tether to unwind during ascent of theUAV, as shown by block 3408.

In practice, the control system may operate the motor to allow thetether to unwind by controlling a maximum current supplied to the motor.By limiting the maximum current supplied to the motor, the controlsystem limits the amount of force that the motor can exert on thetether. More specifically, the control system may limit the maximumcurrent to a small enough value that the motor's maximum upward forceexerted on the tether is smaller in magnitude than the downward force onthe tether due to gravitational forces on the payload. As a result, theUAV may fly upward, and the tether will continue to unwind due to thedownward force on the tether exceeding the upward force from the motor.In other examples, the control system may merely turn off the motor,allowing it to spin freely, in order to obtain similar results.

Further, as noted above, the tether may be disposed on a spool. Morespecifically, a first end of the tether may be non-fixedly wound on thespool. As such, when the tether completely unwinds from the spool, thetether may detach and fall away from the spool. Thus, while the controlsystem operates the motor to allow the tether to unwind, the controlsystem may further cause the UAV to initiate a flight to a differentlocation (e.g., a return location), such that the flight of the UAVunwinds the tether and separates the tether from the spool, therebyreleasing the tether from the UAV, as shown by block 3410. In thismanner, when the payload coupling apparatus is unable to detach from thepayload, both the payload and the tether may be left behind at thedelivery location, allowing the UAV to safely navigate away.

B. Snag Detection

A UAV carrying out tethered pickup and delivery of payloads according tothe processes disclosed herein may find itself operating in variousdifferent types of environments with various different issues toaddress. One issue may involve undesirable or unexpected forces exertedon the tether. For instance, a person may excessively yank on thetether, or the tether might get snagged on a moving or stationaryobject, resulting in a downward force on the tether. Other examples arepossible as well. In these situations, if the downward force is greatenough, the UAV could be pulled out of its flight, perhaps damaging theUAV, the payload, or nearby persons or property. Accordingly, thecontrol system may detect when certain forces are applied to the tetherduring delivery of a payload and responsively take remedial action byallowing the tether to unwind from its spool.

FIG. 35 is a flow chart illustrating a method 3500 of detecting andaddressing undesirable downward forces on a tether when lowering apayload toward the ground. Method 3500 may be carried out by a UAV suchas those described elsewhere herein. For example, method 3500 may becarried out by a control system of a UAV with a winch system. Further,the winch system may include a tether disposed on a spool, a motoroperable in a first mode and a second mode that respectively counter andassist unwinding of the tether due to gravity (e.g., by driving thespool forward or in reverse), a payload coupling apparatus thatmechanically couples the tether to a payload, and a payload latchswitchable between a closed position that prevents the payload frombeing lowered from the UAV and an open position that allows the payloadto be lowered from the UAV.

As shown by block 3502, method 3500 involves the control system of theUAV operating the motor to carry out tethered delivery of a payload(e.g., by performing method 1800). During the process of delivering thepayload to a target location, the control system may detect anundesirable downward force on the tether. As described above, thepresence of additional weight (or in this case, the presence of asufficient downward force) on the tether may result in an increase incurrent supplied to the motor in order to maintain a desired rotationalspeed of the motor. As such, the control system may detect anundesirable downward force on the tether based on the motor current.Further, in order to avoid false positives, the control system may alsoconsider how long the motor current is increased.

Additionally, the control system may consider an unwound length of thetether when detecting an undesirable downward force. For instance, inorder to limit the detection of downward forces to sources at or nearground level (e.g., detecting a person yanking on the tether), thecontrol system may also determine how far the tether has been unwoundfrom the spool in order to determine whether any part of the tether isat or near ground level. Other examples are possible as well.

Thus, in practice, during the process of delivering the payload to atarget location and while the UAV is in flight, the control system maydetermine an unwound length of the tether based on encoder datarepresenting a rotation of the tether spool, and the control system maydetermine a motor current based on a current sensor of the motor or thepower system of the UAV. Further, the control system may determine thatboth (a) the unwound length of tether is greater than a threshold lengthand (b) the motor current of the motor is greater than a thresholdcurrent, for at least a predetermined timeout period, as shown by block3504. Responsive to making such a determination, the control system mayoperate the motor to allow the tether to unwind when the UAV ascends(e.g., as described above with respect to block 3408 of method 3400), asshown by block 3506. And further responsive to making the determination,the control system may cause the UAV to initiate a flight to a differentlocation (e.g., a return location), such that the flight of the UAVunwinds the tether and separates the tether from the spool, therebyreleasing the tether from the UAV, as shown by block 3508. In thismanner, when an undesirable downward force is exerted on the tether, thetether may unwind and detach from the UAV, allowing the UAV to safelynavigate away.

In other examples, rather than detecting a snag and responsivelyoperating the motor to unwind and release the tether, snags may beresolved by imposing a current limit on the motor when picking up apayload. Limiting the motor current to a maximum value limits the amountof force the motor can exert on the tether, which may prevent a UAV fromcrashing if the tether becomes snagged. For instance, if the currentlimit is low enough that the maximum upward force exerted on the tetherby the motor is weaker than a downward force on the tether, then thecurrent limit on the motor may allow the tether to completely unwind anddetach from its spool, should the UAV fly away while the tether issnagged.

In addition to experiencing undesirable forces during delivery of apayload, the tether may also experience undesirable forces during pickupof the payload. For instance, when winching a payload from the groundtoward the UAV, the payload and/or the tether may become snagged onvarious objects, such as trees, buildings, or various other nearbyobjects. As another example, an unexpectedly heavy payload could beattached to the tether, resulting in an excessive downward force on thetether that prevents the UAV from lifting the payload. Accordingly, thecontrol system may detect when certain forces are applied to the tetherduring pickup of a payload and responsively take remedial action.

FIG. 36 is a flow chart illustrating a method 3600 of detecting andaddressing undesirable downward forces on a tether when winching apayload toward a UAV. Method 3600 may be carried out by a UAV such asthose described elsewhere herein. For example, method 3600 may becarried out by a control system of a UAV with a winch system. Further,the winch system may include a tether disposed on a spool, a motoroperable in a first mode and a second mode that respectively counter andassist unwinding of the tether due to gravity (e.g., by driving thespool forward or in reverse), a payload coupling apparatus thatmechanically couples the tether to a payload, and a payload latchswitchable between a closed position that prevents the payload frombeing lowered from the UAV and an open position that allows the payloadto be lowered from the UAV.

As shown by block 3602, method 3600 involves the control system of theUAV operating the motor to carry out tethered delivery of the payload(e.g., by performing method 1700). During a process of picking up thepayload to be delivered, and while the UAV is over or near to a pickuplocation, the control system may determine that a payload couplingapparatus is mechanically coupled to a payload (e.g., based on the motorcurrent as described above with respect to method 1700) and mayresponsively operate the motor to retract the tether and lift thepayload toward the UAV, as shown by block 3604.

While retracting the tether, the control system may detect an errorcondition when the tether and/or the payload becomes snagged. In orderto detect a snag, the control system may monitor the motor current. Asdescribed above, adding a downward force to the tether may cause anincrease in motor current in order to counteract the downward force andmaintain a motor speed set by a speed controller. Thus, when the tetherand/or the payload becomes snagged, the motor current may increase asthe motor attempts to maintain the rotational speed set by the speedcontroller. However, as also noted above with respect to method 1700, anincrease in motor current may be indicative of the payload reaching theUAV after winching is complete. Accordingly, the control system may alsomonitor and consider an unwound length of the tether when detecting asnag. For instance, if the unwound length of the tether indicates thatthe payload has not yet reached the UAV, then the control system maydetect a snag. On the other hand, if the unwound length of the tetherindicates that the payload has reached the UAV, then the control systemmay not detect a snag. Thus, while retracting the tether with thepayload coupled thereto, the control system may detect an errorcondition when both (a) an unwound length of the tether is greater thana threshold length and (b) a motor current of the motor is greater thana threshold current, as shown by block 3606.

In any case, after detecting the error condition, the control system maymake an attempt to correct the error condition by operating the motor tounwind the tether (e.g, by a predetermined length), and may then resumeretracting the tether, as shown by block 3608. Unwinding the tether mayadd slack to the tether, perhaps allowing the weight of the payload toundo the detected snag. In some examples, the control system may causethe UAV to reposition itself before resuming retracting the tether inorder to improve the chances of undoing the snag and/or reduce thechances of encountering the same snag.

If, after resuming the retracting of the tether, the control systemdetects that the error condition is still present (e.g., as shown byblock 3606), the control system may repeat the attempt to correct theerror condition by repeating block 3608, and the control system maymonitor the number of repeated correction attempts. Once the controlsystem determines that a predetermined number of attempts to correct theerror condition have been made without successfully correcting the errorcondition, the control system may responsively end the process ofpicking up the payload and initiate a payload delivery process to returnthe payload to the ground at or near the pickup location, as shown byblock 3610. More specifically, the control system may operate the motorto lower the payload to the ground as if it was performing a payloaddelivery according to method 1800.

C. Failure to Pick Up Payload

Occasionally, when a UAV attempts to pick up a payload for tethereddelivery (e.g., by performing method 1700), the UAV may retract thetether before a payload has been attached to the tether. For instance,while performing method 1700, the control system of the UAV may falselydetermine that a payload is attached to the tether at blocks 1708 and1710 (e.g., due to someone or something pulling on the tether during thepredetermined attachment verification period) and responsively operatethe motor to retract the tether. Accordingly, the control system may beconfigured to determine, during retracting of the tether, that a payloadis not actually attached to the tether.

FIG. 37 is a flow chart of a method 3700 of detecting that the UAVfailed to pick up a payload. Method 3700 may be carried out by a UAVsuch as those described elsewhere herein. For example, method 3700 maybe carried out by a control system of a UAV with a winch system.Further, the winch system may include a tether disposed on a spool, amotor operable in a first mode and a second mode that respectivelycounter and assist unwinding of the tether due to gravity (e.g., bydriving the spool forward or in reverse), a payload coupling apparatusthat mechanically couples the tether to a payload, and a payload latchswitchable between a closed position that prevents the payload frombeing lowered from the UAV and an open position that allows the payloadto be lowered from the UAV.

As shown by block 3702, method 3700 involves the control system of theUAV operating the motor to carry out tethered delivery of the payload(e.g., by performing method 1700). During a process of picking up thepayload to be delivered, and while the UAV is over or near to a pickuplocation, the control system may operate the motor to unwind the tetherand lower a payload coupling apparatus to an expected payload attachmentaltitude, as shown by block 3704. As noted above, the payload attachmentaltitude may be an altitude at which a human, or perhaps a roboticdevice, may grab the payload coupling apparatus for attaching thecoupling apparatus to a payload. For instance, the payload attachmentaltitude may be an altitude less than two meters above ground level.

After lowering the tether, the control system may wait for apredetermined payload attachment period, as shown by block 3706. Thisattachment period allows time for a human, or perhaps a robotic device,to attach a payload to the payload coupling apparatus.

When the payload attachment period ends, the control system may performan attachment verification process, as further shown by block 3706. Inparticular, the attachment verification process may involve the controlsystem operating the motor so as to counter unwinding of the tether fora predetermined attachment verification period (e.g., by pulling upwardson the tether in order to hold the tether in place or retracting thetether at a certain rate), as shown by block 3706 a. The motor currentrequired to hold the tether in place or retract the tether at a certainrate will be greater when the payload is attached, due to the addedweight of the payload. As such, the attachment verification process mayfurther involve the control system determining, based at least in parton motor current during the predetermined attachment verificationperiod, whether or not the payload coupling apparatus is mechanicallycoupled to the payload, as shown by block 3706 b. For instance, asdiscussed above, the control system may determine the motor currentbased on data from a current sensor of the motor or of the power systemof the UAV. If, during the attachment verification process, the motorcurrent exceeds a threshold current value, then the control system maydetermine that the payload is coupled to the payload coupling apparatus.On the other hand, if the motor current is below the threshold currentvalue, then the control system may determine that the payload couplingapparatus is not coupled to the payload.

Further, when the control system determines that the payload couplingapparatus is not mechanically coupled to the payload, the control systemcan cause the UAV to repeat the lowering of the payload couplingapparatus and the attachment verification process in order to reattemptpickup of the payload, and in some embodiments these processes may onlybe repeated up to a predetermined number of times, as shown by block3706. At this point, rather than attempting to pick up the payloadagain, the control system may cause the UAV to abandon the pickup andnavigate away. In practice, for instance, the control system maydetermine that the attachment verification process has been repeated apredetermined number of times without successful coupling of the payloadcoupling apparatus to the payload, and responsively initiate a processto cancel pickup of the payload and initiate flight of the UAV to anext, different location, as shown by block 3708. The different locationmay be another pickup location, or it may be some other location, suchas a UAV dock for docking and/or storing the UAV. Other examples arepossible as well.

As noted above, there may be situations when control system falselydetermines that a payload is attached during the payload verificationperiod, and the control system may responsively cause the motor to entera winching state to retract the tether toward the UAV. Accordingly, inorder to reduce such false determinations, the duration of thepredetermined attachment verification period described above may beincreased. Additionally or alternatively, the control system may befurther configured to perform the attachment verification process andtether lowering process as shown by block 3706 while operating in thewinching state.

D. Payload Latch Failure

As described above with respect to method 1800, when a UAV successfullypicks up a payload and pulls the payload or a payload coupling apparatusinto a receptacle of the UAV, the control system may close a payloadlatch to secure the payload to the UAV. However, there may be situationswhere the control system fails to close the latch (e.g., due to anobstruction or some other issue) or where the control system closes thelatch but the closed latch fails to secure the payload to the UAV.Accordingly, the control system may be configured to determine whetherthe payload latch has successfully secured the payload to the UAV.

In some embodiments, the control system may operate the motor to pullupwards on the tether prior to attempting to close the payload latch. Ifthe payload and/or payload coupling apparatus have reached the UAVreceptacle, the payload coupling apparatus is pressed up against the UAVsuch that the motor cannot retract the tether any further. At thispoint, closing the payload latch may successfully secure the payloadand/or the payload coupling apparatus to the UAV. On the other hand, ifthe payload and/or payload coupling apparatus have not yet reached theUAV receptacle, then the motor may still be retracting the tether, andclosing the payload latch at this point would unsuccessfully secure thepayload. Accordingly, when closing the payload latch and/or for a timeduration after closing the payload latch, the control system may beconfigured to monitor the motor speed to determine whether the payloadlatch successfully closed and secured the payload to the UAV. Forinstance, responsive to detecting that the motor speed is above athreshold speed, the control system may determine that the payload latchfailed to successfully close and/or secure the payload to the UAV.

In other embodiments, after attempting to close the payload latch, thecontrol system may detect payload latch failure by operating the motorto unwind the tether a predetermined length. If the payload latch wassuccessfully closed to engage the payload or payload coupling apparatus,then the payload or payload coupling apparatus may be arranged withinthe UAV receptacle such that all or a portion of the weight of thepayload rests on the payload latch rather than the tether, and the motorcurrent might be below a threshold current (e.g., approximately zero).On the other hand, if the payload latch failed to close, then the weightof the payload might be supported by the tether, and the motor currentrequired to support the weight of the payload might be above a thresholdcurrent. Accordingly, the control system may determine whether thepayload latch successfully closed based on the motor current of the UAV.

In any case, responsive to detecting that the payload latch failed toclose, the control system may operate the motor to winch the payloadback toward the UAV and reattempt closing the latch. This process may berepeated up to a predetermined number of times or until the payloadlatch is successfully closed. After unsuccessfully repeating the processthe predetermined number of times, the control system may responsivelyoperate the motor to lower the payload back to the ground and detach thepayload from the tether (e.g., by performing method 1800).

The following table provides a brief representation of the variousmethods for detecting and resolving errors as described above:

Error Detection Mechanism Responsive Action Upon delivery, packageTether over-run procedure Turn off motor (or reduce gets stuck such thatit attempted a predetermined motor current limit to lower can't bereleased number of times without level) such that tether from payloadcoupling success. unwinds and eventually apparatus. detaches from spool,as UAV flies upward and/or away. Payload and/or payload Payloadre-lowering and Enter the DESCENDING coupling apparatus snag winchingback up attempted state 3822 (see FIG. 38B) during package pick-uppredetermined number of of the delivery mode in order (after payloadattached, times without success. to return package to ground at whilewinching payload [Winching failure detected pickup location. up to UAV)when motor current > threshold AND unwound tether length > threshold(possibly after timeout period, perhaps using a Schmitt trigger toreduce detection error)] Payload and/or payload Motor current >threshold Try to lower payload and/or coupling apparatus snag ANDunwound tether length > payload coupling apparatus as tether is beingthreshold (possibly after (similar to over-run for retracted afterdelivery timeout period, perhaps using payload release on ground),(after payload should a Schmitt trigger to reduce repeat a predeterminedhave been released) detection error) number of times, and then let thecapsule and tether go (by turning off the motor or reducing the currentlimit such that the tether unwinds and detaches from the spool) and flyaway. OR Impose a low motor current limit during tether retraction suchthat a snag causes the tether to unwind and eventually detach from thespool as the UAV flies away. During payload pickup Lower tether toappropriate After making maximum process, failure to height for pickup,and if number of attempts without mechanically couple motor current <threshold, success, abort pickup and fly payload to payload then repeat.away. coupling apparatus.

XIII. EXAMPLE STATE DIAGRAM OF A UAV

FIGS. 38A-38C illustrates an example state diagram 3800 of a UAVcarrying out one or more of the various processes described herein. Asshown, the UAV may occasionally operate in an IDLE state 3802. In theIDLE state, the payload latch may be in the closed position such thatthe tether is prevented from unwinding. Further, in order to keep themotor stationary, the speed controller may set a desired operationalspeed of the motor that corresponds to a tether descent rate of 0 m/s,and the control system may ignore accumulated error over time whenadjusting the motor current to match the desired operational speed. Themotor current may be limited to a very high value or may have no limitat all, as the motor is not expected to rotate during this state. Insome examples, the UAV may enter the IDLE state 3802 when transporting apayload from a source location to a target location, or when navigatingto a source location for pickup. Additionally, the UAV may enter theIDLE state 3802 from any state responsive to receiving a stop command.Other examples are possible as well.

Once the UAV reaches a source location for pickup of a payload, thecontrol system may receive a command to pick up the payload and mayresponsively enter a payload pickup mode (e.g., by performing method1700). As shown by state diagram 3800, the payload pickup mode mayinclude a LOWERING HOOK state 3804, during which the control systemoperates the motor to unwind the tether from a spool and lower a payloadcoupling apparatus toward the ground. While state 3804 refers to thepayload coupling apparatus as a hook, the payload coupling apparatus cantake various forms, as discussed above. The payload coupling apparatusmay be lowered to a predetermined payload attachment altitude based onthe altitude of the UAV. Once the payload coupling apparatus reaches thepayload attachment altitude (e.g., when the control system determinesthat the length of the unwound tether is at least a threshold length),the control system may cause the UAV to enter a WAITING FOR PAYLOADstate 3806 for a time delay, during which the control system operatesthe motor to hold the payload coupling apparatus at a substantiallyconstant altitude, thereby allowing the payload to be attached to thepayload coupling apparatus. Additionally, if the control system fails todetermine that the payload coupling apparatus has been lowered to thepredetermined payload attachment altitude within a set time period(e.g., a timeout period), the control system may responsively advance tothe WAITING FOR PAYLOAD state 3806.

From the WAITING FOR PAYLOAD state 3806, once the time delay elapses,the control system enters a VERIFY PAYLOAD state 3808. During thisstate, the control system determines whether the payload is attached tothe payload coupling apparatus based on a motor current supplied to themotor when the motor attempts to hold the payload coupling apparatus ata constant altitude or begins to retract the tether toward the UAV. Ifthe motor current is below a threshold current during the VERIFY PAYLOADstate 3808, the control system returns to the LOWERING HOOK state 3804to reattempt attachment of the payload. As described above with respectto method 3700, this repetition may be repeated a number of times untila limit is reached. Once the limit is reached, the control system maycause the UAV to retract the tether, ascend, and perhaps return to theIDLE state 3802 from which the UAV may navigate to some other location.

On the other hand, if, during the VERIFY PAYLOAD state 3808, the controlsystem determines that the payload has been attached to the payloadcoupling apparatus (e.g., by determining after a time delay that themotor current is at least a threshold current), the control system mayenter a WINCHING PAYLOAD state 3810. During this state, the controlsystem may operate the motor to retract the tether and pull the payloadtoward the UAV. As described above with respect to method 3700, thecontrol system may also monitor motor current in this state to determinewhether a false positive was obtained during the VERIFY PAYLOAD state3808 (e.g., by detecting that the motor current is threshold low).Additionally, as noted above with respect to method 3600, the controlsystem may monitor the motor current during the WINCHING PAYLOAD state3810 in order to detect when the tether becomes snagged (e.g., bydetecting that the motor current is threshold high). Responsive todetecting a snag, the control system may operate the motor to lower thepayload a predetermined length and reattempt winching the payload. Aftera threshold number of attempts to remove the snag, the control systemmay operate the motor to lower the payload to the ground and abandonpickup of the payload. This may involve advancing to a DESCENDING state3822, which is discussed in more detail below.

While operating in the WINCHING PAYLOAD state 3810, if no snags aredetected, or if all detected snags are resolved, the control system maydetect that the payload is within a threshold distance of the UAV (e.g.,by measuring a number of rotations of the tether spool) and responsivelyenter an ENGAGING PAYLOAD state 3812. During this state, the controlsystem may increase the current supplied to the motor for apredetermined time period in order to attempt to pull the payload into,and orient the payload within, a receptacle of the UAV. If, during thisstate, the control system detects that the motor current is below athreshold current and/or that the tether is unwound at least a thresholdlength, then the control system may responsively determine that thepayload is too far from the UAV and may re-enter the WINCHING PAYLOADstate 3810 until the control system again detects that the payload isclose enough to the UAV to advance to the ENGAGING PAYLOAD state 3812.

On the other hand, if, during the ENGAGING PAYLOAD state 3812, the motorcurrent remains threshold high and the unwound length of the tetherindicates that the payload has reached the UAV, then the control systementers the LATCHING PAYLOAD state 3814. During this state, the controlsystem switches the payload latch to the closed position, therebypreventing the tether and/or the payload from descending from the UAV.As described above, the control system may determine whether the payloadlatch was successfully closed by monitoring the motor speed and/or byoperating the motor to attempt to lower the payload and monitoring themotor current. If the control system determines that the payload latchwas not successfully closed, the control system may return to theWINCHING PAYLOAD state 3810 and reattempt to lift and engage thepayload. But if the control system determines that the payload latch wassuccessfully closed, then the control system may enter a WAITING TODELIVER state 3816.

The WAITING TO DELIVER state 3816 may be similar to the IDLE state 3802where the payload is secured to the UAV, and the control system operatesthe motor to keep the payload stationary. If, after a time delay, thecontrol system detects that the motor speed is greater than a thresholdspeed, this may indicate that the payload is not sufficiently secured tothe UAV, and the control system may responsively return to the WINCHINGPAYLOAD state 3810. Otherwise, entering the WAITING TO DELIVER state3816 signals the end of the pickup mode.

While in the WAITING TO DELIVER state 3816, the control system mayreceive a command to deliver the payload and may responsively enter adelivery mode (e.g., by performing method 1800). The delivery mode mayinclude a PRE-DROP TENSION state 3818. In this state, while the payloadlatch is closed, the control system may operate the motor to lift thepayload (e.g., by setting the desired tether speed to 1 m/s or someother speed in an upward direction, or by setting the motor current to apredetermined value), thereby removing the weight of the payload fromthe payload latch and making it easier to open the payload latch. Whilein the PRE-DROP TENSION state 3818, the control system may open thepayload latch and advance to the POST-DROP TENSION state 3820 after atime delay. In this state, the control system may operate the motor tohold the tether in a constant position for a predetermined amount oftime to allow the weight of the payload to pull the payload firmlyagainst the payload coupling apparatus, thereby reducing any chance thatthe payload might slip off and detach from the payload couplingapparatus. After the predetermined amount of time has passed, thecontrol system may enter the DESCENDING state 3822.

In both the PRE-DROP TENSION state 3818 and the POST-DROP TENSION state3820, if the control system detects that the payload has traveled atleast a threshold distance (e.g., by measuring rotation of the spool),then this may indicate that an error has occurred (e.g., prematuredetachment of the payload from the payload coupling apparatus orsnapping of the tether) because the spool should remain substantiallymotionless during these states. As a result to detecting such an error,the control system may return to the IDLE state 3802 and cause the UAVto navigate to a location where it may be serviced.

In the DESCENDING state 3822, the control system may operate the motorto unwind the tether according to a predetermined descent profile thatspecifies a constant or varying operational speed of the motor. Upondetecting that the tether has unwound at least a predetermined amount(e.g., detecting that the payload is within a threshold distance of theground based on an altitude of the UAV), the control system may enter aWAITING FOR TOUCHDOWN state 3824. In some examples, the control systemmay also be configured to advance from the DESCENDING state 3822 to theWAITING FOR TOUCHDOWN state 3824 if a threshold amount of time elapsesin the DESCENDING state 3822 without advancing to the WAITING FORTOUCHDOWN state 3824.

In the WAITING FOR TOUCHDOWN state 3824, the control system may monitorthe motor current and its operational speed in order to detect whetherthe payload has reached the ground. Specifically, upon determining thatboth the motor current and the motor speed are threshold low, thecontrol system may enter a POSSIBLE TOUCHDOWN state 3826 to verify thatthe payload has in fact reached the ground. The control system may beconfigured to remain in the POSSIBLE TOUCHDOWN state 3826 for apredetermined amount of time. If, during that time, either the motorcurrent or the motor speed becomes threshold high, this may indicatethat the payload has not yet reached the ground, and the control systemmay return to the WAITING FOR TOUCHDOWN state 3824. However, if, duringthe duration of the POSSIBLE TOUCHDOWN state 3826, the motor current andthe motor speed remain threshold low, this may indicate that the payloadhas in fact reached the ground, and the control system may responsivelyadvance to a TOUCHED DOWN state 3828. In some examples, the controlsystem may also be configured to advance from the WAITING FOR TOUCHDOWNstate 3824 to the TOUCHED DOWN state 3828 if a threshold amount of timeelapses in the WAITING FOR TOUCHDOWN state 3824 without advancing to thePOSSIBLE TOUCHDOWN state 3826.

Once in the TOUCHED DOWN state 3828, the control system may operate themotor to cause over-run of the tether such that the payload couplingapparatus continues to lower while the payload remains stationary on theground. Continuing to lower the payload coupling apparatus may cause thepayload coupling apparatus to detach from the payload. After causingtether over-run for a predetermined amount of time, the control systemmay enter a VERIFY RELEASE state 3830 in order to determine whether thepayload coupling apparatus did in fact separate from the payload.

In the VERIFY RELEASE state 3830, the control system may operate themotor to pull upwards on the tether. Based on the motor current whenpulling upwards on the tether, the control system may determine whetheror not the payload has been released from the payload couplingapparatus. If the motor current is threshold high, this may indicatethat the payload is still attached, and the control system may return tothe TOUCHED DOWN state 3828. This process may be repeated up to apredetermined number of times, at which point the control system mayenter a FREE SPIN state 3832.

In the FREE SPIN state 3832, the control system may operate the motor toallow the tether to completely unwind such that the tether disconnectsand falls away from the UAV. This may be achieved by limiting the motorcurrent to a sufficiently low value that the motor is unable tocounteract the downward force on the tether caused by the gravitationalpull on the payload. Alternatively, the motor can be shut off completely(e.g., limiting the motor current to 0A).

Referring back to the VERIFY RELEASE state 3830, if, throughout apredetermined duration, the motor current remains threshold low, thismay indicate that the payload has in fact separated from the payloadcoupling apparatus, and the control system may responsively advance toan ASCENDING state 3834.

In the ASCENDING state 3834, the control system may operate the motor toretract the tether and the payload coupling apparatus up toward the UAVaccording to a predetermined ascent profile that specifies a constant orvarying operational speed of the motor. Once the control systemdetermines that an unwound length of the tether is below a thresholdlength such that the payload coupling apparatus is sufficiently close tothe UAV (e.g., based on a measured number of rotations of the spool),the control system may enter an ASCENDING PAUSE state 3836.

In the ASCENDING PAUSE state 3836, the control system may operate themotor to halt the retraction of the tether. Once retraction of thetether is halted, the control system may control a movement of the UAVin order to dampen any oscillations of the tether that may have occurredduring the ASCENDING state 3834. After damping the tether oscillations,the control system may enter a FINAL ASCENT state 3836.

In the FINAL ASCENT state 3836, the control system may operate the motorto resume retracting the tether. However, in this state, the tether maybe retracted at a slower rate than that of the ASCENDING state 3834.This slower rate may introduce weaker oscillations on the tether. Alsoduring the FINAL ASCENT state 3836, the control system may monitor themotor current to determine when the payload coupling apparatus reachesthe UAV. In practice, when the payload coupling apparatus reaches theUAV, the apparatus is pressed against the UAV, the motor speed drops tozero, and the motor current increases in an attempt to increase motorspeed. Accordingly, the control system may determine that the payloadcoupling apparatus has reached the UAV based on the motor currentexceeding a threshold current. Responsively, the control system mayenter an ENGAGING state 3840.

In the ENGAGING state 3840, the control system may increase the maximummotor current in order to allow the motor to pull the payload couplingapparatus into, and orient itself within, a receptacle of the UAV. Oncethe payload coupling apparatus is secured within the receptacle, thecontrol system may return to the IDLE state 3802. If, during theENGAGING state 3840, the motor current falls below a threshold current,this may indicate that the payload coupling apparatus was not in factnear to the UAV, and the detected increase in current was likely causedby something else (e.g., a temporary snag of the tether). In such ascenario, the control system may revert back to the FINAL ASCENT state3838.

As shown by the state diagram 3800, once the control system enters theASCENDING state 3834, the control system may repeatedly advance to thenext state upon determining that a threshold amount of time has elapsedwithout advancing states.

In some examples, a lower maximum current limit may be imposed on theUAV motor when retracting the tether, as shown by states 3834 to 3840,when compared to lowering the tether, as shown by states 3818 to 3828.This is because the tether is more likely to encounter a snag whenretracting the tether. Imposing a lower current limit reduces the amountof force that the motor may exert on the tether. This may prevent themotor from causing the UAV to crash by continuing to winch the UAVtoward a snag. And as noted above, if the current limit is low enoughthat the maximum force of the motor is weaker than a downward force onthe tether, then the current limit on the motor may allow the tether tocompletely unwind and detach from its spool, should the UAV fly awaywhile the tether is snagged. Similar methods may be employed wheninitially picking up a payload during states 3806 to 3814.

XIV. ADDITIONAL ASPECTS

In some embodiments, the control system of the UAV may be configured tocalibrate the rotary encoder and speed controller of the motor uponstartup of the system. In practice, when the UAV system is initiallypowered on, the motor should be stationary. Accordingly, the encoderdata should also indicate that the motor is stationary. If the encoderdata indicates otherwise, then an offset may be applied to the encoderdata to account for any inconsistencies.

The control system may further test the friction of the motor on startupof the UAV system. Based on the measured motor friction, an offset maybe applied to various motor current settings to account for the measuredmotor friction. Over time, the friction of a DC motor may vary.Therefore, measuring friction on every startup and adjusting motorcurrent settings accordingly may enable consistent operation over thelife of the motor.

XV. CONCLUSION

The particular arrangements shown in the Figures should not be viewed aslimiting. It should be understood that other implementations may includemore or less of each element shown in a given Figure. Further, some ofthe illustrated elements may be combined or omitted. Yet further, anexemplary implementation may include elements that are not illustratedin the Figures.

Additionally, while various aspects and implementations have beendisclosed herein, other aspects and implementations will be apparent tothose skilled in the art. The various aspects and implementationsdisclosed herein are for purposes of illustration and are not intendedto be limiting, with the true scope and spirit being indicated by thefollowing claims. Other implementations may be utilized, and otherchanges may be made, without departing from the spirit or scope of thesubject matter presented herein. It will be readily understood that theaspects of the present disclosure, as generally described herein, andillustrated in the figures, can be arranged, substituted, combined,separated, and designed in a wide variety of different configurations,all of which are contemplated herein.

We claim:
 1. A system comprising: a winch system for an aerial vehicle, wherein the winch system comprises: (a) a tether disposed on a spool, wherein a leading end of the tether is mechanically couplable a payload, and (b) a motor that is operable to apply torque to the tether; at least one sensor arranged to generate sensor data indicative of oscillations of the tether when the tether is at least partially unwound; and a control system operable to: while the aerial vehicle is in a hover flight mode, enabling a tether retraction mode for retraction of the tether; and while operating in the tether retraction mode: use the generated sensor data as a basis for detecting oscillation of the tether; and perform a damping routine to dampen oscillations of the tether, wherein the damping routine comprises responding to detection of oscillation exceeding a threshold by: (a) while the aerial vehicle is in a position-hold mode, causing the aerial vehicle to reduce an extent of flight stabilization along at least one of the three dimensions, or (b) causing the aerial vehicle to switch from the hover flight mode to a forward flight mode in which movement of the aerial vehicle results in drag on the payload coupling apparatus.
 2. The system of claim 1: wherein the damping routine comprises causing the aerial vehicle to switch from the hover flight mode to the forward flight mode in which movement of the aerial vehicle results in drag on the payload coupling apparatus, and wherein the control system is further operable to: pause retraction of the tether; based at least in part on the sensor data, detect that oscillations of the payload coupling apparatus have been sufficiently dampened by the drag; and in response to detecting that oscillations of the payload coupling apparatus have been sufficiently dampened by the drag, resume retraction of the tether to lift the payload coupling apparatus to the aerial vehicle.
 3. The system of claim 1, wherein the aerial vehicle is operable in the position-hold to substantially maintain a physical position during hover flight by engaging in flight stabilization along three dimensions in physical space, and wherein the damping routine comprises, while the aerial vehicle is in the position-hold mode, causing the aerial vehicle to reduce the extent of flight stabilization along at least one of the three dimensions, thereby resulting in damping of the oscillations due to energy dissipation during movement of the aerial vehicle along the at least one dimension.
 4. The system of claim 1, wherein the motor being operable to apply torque to the tether comprises the motor being operable in both a first mode and a second mode to apply torque to the tether in a winding direction and an unwinding direction, respectively, wherein operation in the tether retraction mode comprises at least operating the motor in the first mode to retract the tether at a retraction rate, and wherein the damping routine comprises, while operating in the tether retraction mode, operating the motor to vary the retraction rate based on the detected oscillation.
 5. A method comprising: causing, by a computing device, an aerial vehicle to operate in a hover flight mode, wherein the aerial comprises a winch system operable to lower a tether disposed on a spool, from from the aerial vehicle towards the ground, wherein the winch system comprises: (a) the tether, (b) a motor that is operable to apply torque to the tether, and (c) a payload coupling apparatus coupled to a leading end of the tether and structured to mechanically couple a payload to the tether; while the aerial vehicle is in a hover flight mode and the tether is lowered, enabling a tether retraction mode for retraction of the tether; while operating in the tether retraction mode, the computing device: receiving sensor data indicative of oscillations of the payload coupling apparatus; using the sensor data as a basis for detecting oscillation of the payload coupling apparatus; and performing a damping routine to dampen oscillations of the payload coupling apparatus, wherein the damping routine comprises responding to detection of payload oscillation exceeding a threshold by: (a) while the aerial vehicle is in a position-hold mode, causing the aerial vehicle to reduce an extent of flight stabilization along at least one of the three dimensions, or (b) causing the aerial vehicle to switch from the hover flight mode to a forward flight mode in which movement of the aerial vehicle results in drag on the tether.
 6. The method of claim 5, wherein performing the damping routine further comprises: pausing retraction of the tether; based at least in part on the sensor data, determining that oscillations of the payload coupling apparatus have been sufficiently dampened by the drag; and in response to detecting that oscillations of the payload coupling apparatus have been sufficiently dampened by the drag, resuming retraction of the tether to lift the payload coupling apparatus to the aerial vehicle.
 7. The method of claim 5, wherein the aerial vehicle is operable in the position-hold to substantially maintain a physical position during hover flight by engaging in flight stabilization along three dimensions in physical space, and wherein performing the damping routine comprises, while the aerial vehicle is in the position-hold mode, causing the aerial vehicle to reduce the extent of flight stabilization along at least one of the three dimensions, thereby resulting in damping of the oscillations due to energy dissipation during movement of the aerial vehicle along the at least one dimension.
 8. The method of claim 5, wherein the payload is a payload coupling apparatus coupled to a leading end of the tether and structured to mechanically couple another payload.
 9. The method of claim 5, wherein the motor being operable to apply torque to the tether comprises the motor being operable in both a first mode and a second mode to apply torque to the tether in a winding direction and an unwinding direction, respectively, wherein operation in the tether retraction mode comprises at least operating the motor in the first mode to retract the tether at a retraction rate, and wherein the damping routine comprises, while operating in the tether retraction mode, operating the motor to vary the retraction rate based on the detected oscillation.
 10. A method comprising: causing, by a computing device, an aerial vehicle to operate in a hover flight mode, wherein the aerial vehicle comprises a winch system including: (a) a tether disposed on a spool and (b) a motor that is operable to apply torque to the tether; while the aerial vehicle is in a hover flight mode, enabling a tether retraction mode for retraction of the tether; and while operating in the tether retraction mode, the computing device: receiving sensor data indicative of oscillations of the payload; determining, by the computing device, based at least in part on sensor data, that the detected oscillations exceed a threshold; and responsive to determining that the detected oscillations exceed the threshold, the computing device causing the aerial vehicle to switch from the hover flight mode to a forward flight mode in which movement of the aerial vehicle results in drag on a payload that is coupled to the tether, wherein the drag dampens oscillations of the payload when the tether is at least partially unwound.
 11. The method of claim 10 wherein the payload is a payload coupling apparatus coupled to a leading end of the tether and structured to mechanically couple another payload.
 12. The method of claim 10, wherein the motor is operable in a first mode and a second mode to apply torque to the tether in a winding direction and an unwinding direction, respectively, and wherein the control system is further operable to: retract the tether by operating the motor in the first mode; based at least in part on the sensor data, detect that oscillations of the payload exceed a threshold; while the detected oscillations exceed the threshold, operate the motor to pause retraction of the tether; based at least in part on the sensor data, detect that oscillations of the payload have been sufficiently dampened by the drag; and in response to detecting that oscillations of the payload have been sufficiently dampened by the drag, operate the motor in the first mode to resume retraction of the tether.
 13. A method comprising: causing, by a computing device, an aerial vehicle to operate in a position-hold mode in which the aerial vehicle substantially maintains a physical position by engaging in flight stabilization along three dimensions in physical space, wherein the aerial vehicle comprises a winch system including: (a) a tether disposed on a spool and (b) a motor that is operable to apply torque to the tether; receiving sensor data indicative of oscillations of the payload; while the aerial vehicle is in the position-hold mode, determining, by the computing device, based at least in part on the sensor data, that oscillations of the payload exceed a threshold; and responsive to determining that the detected oscillations exceed the threshold, the computing device causing the aerial vehicle to reduce an extent of flight stabilization along at least one of the three dimensions, thereby resulting in damping of oscillations of a payload due to energy dissipation during movement of the aerial vehicle along the at least one dimension.
 14. The method of claim 13, wherein causing the aerial vehicle to reduce the extent of flight stabilization is performed while the tether is at least partially unwound.
 15. The method of claim 13, wherein the payload is coupled to a leading end of the tether.
 16. A method comprising: receiving, by a computing device, sensor data indicative of oscillations of a payload, wherein the payload is coupled to a tether of an aerial vehicle, wherein the aerial vehicle comprises a winch system including: (a) the tether disposed on a spool and (b) a motor that is operable to apply torque to the tether; determining, by the computing device, based at least in part on the generated sensor data, one or more factors associated with oscillation of the tether; while the tether is at least partially unwound, the computing device selecting, based at least in part on the one or more factors associated with oscillation of the tether, one or more damping routines from a plurality of available damping routines to dampen oscillations of the payload; and performing the one or more selected damping routines.
 17. The method of claim 16, wherein the plurality of available damping routines include a damping routine comprising: causing the aerial vehicle to switch from a hover flight mode to a forward flight mode in which movement of the aerial vehicle results in drag on the payload, wherein the drag dampens the oscillations of the payload.
 18. The method of claim 16, wherein the aerial vehicle is operable in a position-hold mode in which the aerial vehicle substantially maintains a physical position during hover flight by engaging in flight stabilization along three dimensions in physical space, and wherein the plurality of available damping routines include a damping routine comprising: causing the aerial vehicle to reduce an extent of flight stabilization along at least one of the three dimensions, thereby resulting in damping of the oscillations due to energy dissipation during movement of the aerial vehicle along the at least one dimension.
 19. The method of claim 16, wherein the motor being operable to apply torque to the tether comprises the motor being operable in both a first mode and a second mode to apply torque to the tether in a winding direction and an unwinding direction, respectively, wherein the motor is operable in the first mode to retract the tether at a retraction rate, wherein the motor is operable in the second mode to deploy the tether at a deployment rate, and wherein the plurality of available damping routines include a damping routine comprising operating the motor to vary one or more of the retraction rate and the deployment rate.
 20. The method of claim 16, wherein the control system is further operable to determine a target path of the payload during one or more of unwinding and winding of the tether, and wherein the plurality of available damping routines include a damping routine comprising: based at least in part on the generated sensor data, determining a position of the payload relative to the target path; based on the determined position of the payload relative to the target path, determining a movement to be performed by the aerial vehicle so as to move the payload closer to the target path; and causing the aerial vehicle to perform the determined movement. 